Where's a good place to find a pre 1958 track/path frame

flashes

I'm looking to buy a 21-22" pre 1958 path or track frame to ride End to End in a few year's time when I'm 60. I've been looking at Flea bay, but not seen anything that ticked all the boxes, so apart from the classifieds here, where else should I look???
Ta..

cycleclinic

They come up from time to time. I am looking for a pre wwI path racer. That is harder.

ugo.santalucia

What are the boxes it needs to tick?
I have a 120 mm rear end Claude Butler (52 size, so just under 21 inches) which could make a fixed/track bike, but it's a road frame otherwise... I think it's more early 60s though and I have butchered the rear bridge to fit a brake caliper