As you have done a lot of research work already, I wondered about any other method that might reduce the civil parishes to a manageable few by just searching a Co Down website for McAllister, McBlain, McRobert, Muir and if you were really lucky finding all in the one parish or in a close focus with neighbouring parishes only.
So having a short list of the most likely civil parishes to search, what records would you choose to search or which records would be the quickest. the national census substitutes include the
Flax growers of Ireland,1796 but doesn’t include any of the names, the next is the
Tithes Applotment Books about 1824-1836, which again has a limited inclusion, but worse still the three parishes Holywood , Newtownards and Newry are not well represented at all. Indeed so badly and discovering Newry was listed in 1840, that I drop the tithes for the time being. The next is
Griffiths valuation c~1860McAllister ...McBlain ....McRobert .....McRoberts ........Muir
Aghaderg ----------------- ----------------- ----------------- -----------------
Annaclone ----------------- ----------------- ----------------- -----------------
Ballywalter ----------------- ----------------- ----------------- -----------------
Blaris ----------------- ----------------- ----------------- -----------------
Comber ----------------- ----------------- Comber -----------------
Donaghcloney----------------- ----------------- ----------------- -----------------
----------------- ----------------- ----------------- Down -----------------
Dromara ----------------- ----------------- Dromara -----------------
----------------- ----------------- Dromore Dromore -----------------
Drumballyroney----------------- ----------------- Drumballyroney -------------
----------------- ----------------- ----------------- Dundonald -----------------
----------------- ----------------- ----------------- Garvaghy -----------------
Hillsborough ----------------- ----------------- ----------------- -----------------
Holywood Holywood ----------------- Holywood -----------------
Kilcoo ----------------- ----------------- ----------------- -----------------
Kilkeel ----------------- ----------------- ----------------- -----------------
----------------- ----------------- ----------------- Killinchy -----------------
----------------- ----------------- Kilmore Kilmore -----------------
----------------- ----------------- ----------------- ----------------- Magheradrool
----------------- ----------------- ----------------- Magherally -----------------
Newry Newry ----------------- Newry -----------------
Newtownards Newtownards Newtownards-----------------
----------------- ----------------- ----------------- Saintfield -----------------
Seapatrick ----------------- ----------------- ----------------- -----------------
you might agree that means
Holywood , Newtownards and Newry are the most likely parishes from this one source
If you did the same using perhaps
Ros Davies website you will have many more parishes but the result would be more accurate
so having a short list of the most likely civil parishes to search, what records would you choose to search or which records would be the quickest. the national census substitutes include the
Flax growers of Ireland,1796 but doesn’t include any of the names, the next is the
Tithes Applotment Books about 1824-1836, which again has a limited inclusion, but worse still the three parishes Holywood , Newtownards and Newry are not well represented at all. Indeed so badly and discovering Newry was listed in 1840, that I drop the tithes for the time being.
so going for an easier possibility an existing family tree do you know about
Genes Reunited below? and if you are not one of the treeholders, have you had contact with one of them?
http://www.GenesReunited.co.uk/Mary McBlain 1816 Co Down Ireland ... Ronald
Mary McBlain 1815 County Down Ireland ... Moira
Mary McBlain 1815 Ireland ... Jo and Stuart
Mary McBlain 1815 Ireland ... Barbara
Mary McBlain 1815 Couny Down,Ireland ... Nick
Mary McBlain 1815 Ireland ... Christine
Mary McBlain 1815 Co Down Ireland ... Peter
David McBlain 1811 S Ireland Drogheda ... Kevin
John McBlain 1790 Ireland ... Jo and Stuart
John McBlain 1787 Ireland ... Nick
John McBlain 1785 Ireland ... Moira
James McBlain 1770 Ireland ... Liesele
I need to ask did you check
1840 census in Scotland yourself, ie is all possible clues as to were in Co down are checked out, even in later census
John McBlain whole family must have gone to Lanarkshire Finally my ear thinks Muir in Co Down could be pronounced Moore/ Mure
good luck hoping you knock the bricks flying