This is the full "Brush Manufacturers — Hair" section of the 1939 London yellow pages, but none of them are in north London:-
Casscelloid, Ltd., 60-61, Chiswell St., E.C.1
Chambers Bros. (Tortoiseshell, Ivory, Woods), Showroom: 27 Gt. Pulteney St., W.1; Factory: 163 Brunswick Rd., E.14
Harrisson, J. S., & Sons, Ltd., 1 Chalgrove Rd., E.9 and 8 Foster Lane, E.C.2
Mason Pearson Selling Agency, Ltd., 61 New Oxford St., W.C.1
Neuhafer, M., Levi, Ltd., 28/29 London Wall, E.C.2
"N" postal districts entries in the general "Brush Manufacturers" section:-
Archer, W. & F. (1935) Ltd., Brettenham Rd., N.18
Austin & Fryatt, 2 Kelvin Rd., N.5
Baker, Percy P., 28/36 Orsman Rd., Kingsland Rd., N.1
Bell Brush Co., rear of 19/21, Conewood St., N.5
Burton, A. E., & Sons, 57 Balls Pond Rd., N.1
Culmer, T. W., & Sons, (Shaving), Culmark Works, Vale Rd., N.4
Elephant Brush Co., Ltd., 11/13, Redvers Rd., N.22
Fuldex Brush Works, Ltd., 82 Sunbeam Rd., N.W.10
Hayward, E. W., Penton Brush Works, Cricklewood, N.W.2
Hill Bros, Brushes, Ltd., Edgware Rd., Cricklewood, N.W.2
Kleen-e-ze Brush Co., Ltd., 227 Seven Sisters Rd., N.4 (one of several sales offices)
Luson, A., & Sons, Ltd., Standard Rd., N.W.10
Mares, J., & Sons, 30 Archibald Rd., N.7
Marsh Alfred, Ltd., 62 Pentonville Rd., N.1
Morris & Fordran, Ltd., 54 Rushton St., New North Rd., N.1
Purchase, Hayward, & Co., 469 Hornsey Rd., N.19
Root, James & Son, Tudor Chambers, Station Rd., N.22
Star Brush Co., Ltd., Eden Grove, Holloway, N.7
Underwood, H. W., & Son, 61 Halliford St., N.1
Woolf, John, & Son, Ltd., 178 High Rd., N.W.10