marriage downes williams help

[furzefarm]

I am trying to find the marriage of thomas downes a tailor b1816 mordiford herefordshire to elizabeth williams b 1814 0vermonnow monmouthshire between 1830 and 1840
Their first child Sarah was born in 1837 and census returns say she was baptised in hereford but i cannot find that either. other children were baptised in overmonnow and birmingham they lived in birmingham these I can find
help!!!
furzefarm