eBay and Craigslist finds

I follow these Italian groups:

Bicivintage Eroica:
https://www.facebook.com/groups/623789987663669/

Due ruote vintage:
https://www.facebook.com/groups/978449078916955/

Neo Retro Velo (non Italian):
https://www.facebook.com/groups/neoretrovelo/

STEEL IS REAL -- Classic vintage road bikes (non Italian):
https://www.facebook.com/groups/42851702426/

Acciaio solo corsa:
https://www.facebook.com/groups/acciaiosolocorsa/

Italian steel bike for sale (this is mainly a one-guy Facebook shop):
https://www.facebook.com/groups/589085971245310/

Classic Speedbikes (non Italian):
https://www.facebook.com/groups/classic.speedbikes/

VECCHIE BICI EROICHE (very old bikes usually):
https://www.facebook.com/groups/1508265872723739/

Vintage bicycles:
https://www.facebook.com/groups/290012861095285/

Also the VCC has this handy list:

List of NVCC Groups available to you for various interests of study etc.
Cycle Chic
https://www.facebook.com/groups/724680964290142/
NVCC (for Veteran Cycles)
https://www.facebook.com/groups/518253051619333/
NVCC (for Veteran Tricycles)
https://www.facebook.com/groups/825721027475886/
NVCC (for Pashley & BSA Para- Frames)
https://www.facebook.com/groups/371988756293970/
NVCC (for Early Cycle Shops & Makers)
https://www.facebook.com/groups/534917359948365/
NVCC (for Dursley & New Pedersen)
https://www.facebook.com/groups/1563673610542036/
NVCC (for Early Cycle & Tricycle Lamps, Bells & Accessories)
https://www.facebook.com/groups/280792202116158/
NVCC (for Elswick Cycles Barton on Humber)
https://www.facebook.com/groups/792566257446347/
NVCC (for Elswick Cycles Newcastle Upon Tyne
https://www.facebook.com/groups/1493661580881664/
NVCC (for Victorian, Edwardian & Roaring Twenties Cycle Photos)
https://www.facebook.com/groups/646843032097757/
NVCC (for Velocipede - Boneshaker & Hobby Horse)
https://www.facebook.com/groups/861348290573329/
NVCC (for Humber Cycles pre- Raleigh)
https://www.facebook.com/groups/674534372643631/
NVCC (for Delivery & Work Bicycles & Tricycles)
https://www.facebook.com/groups/1382436922079483/
NVCC (for Scrapbook Cuttings, Odds & Sods)
https://www.facebook.com/groups/440680256098486/
NVCC (for Cycle Speedway)
https://www.facebook.com/groups/1379189735744560/
NVCC (for BSA Cycles)
https://www.facebook.com/groups/412200435637934/
NVCC (for Veteran Tandem Cycles)
https://www.facebook.com/groups/852687541516989/
NVCC (for Hercules Cycles)
https://www.facebook.com/groups/1702572406628317/
NVCC (for Sunbeam Cycles)
https://www.facebook.com/groups/1241267379220980/
NVCC (for Singer & Co Ltd)
https://www.facebook.com/groups/1757110354512649/
NVCC (for Gormully & Jeffery)
https://www.facebook.com/groups/543828412456051/
NVCC for (Hillman Herbert & Cooper)
https://www.facebook.com/groups/1606263496261086/
NVCC (for Coventry Cycles)
https://www.facebook.com/groups/922453784540340/
NVCC (for Pickering & Davis)
https://www.facebook.com/groups/1667032086879628/
NVCC (for Sturmey Archer)
https://www.facebook.com/groups/606542409523483/
NVCC (for New Hudson)
https://www.facebook.com/groups/623155037843721/
NVCC (for Posters, Art & Enamel Signed)
https://www.facebook.com/groups/911010962328280/
NVCC (for Rudge Cycles)
https://www.facebook.com/groups/1692346760999007/
(A request to join any one individual group is required).