i know this thread is kinda old but i found it interesting so here's my two cents.
go to events that cater to your interests, locate the promoter and ask for any promotional items that might be left over. they will usually let you have them to keep from having to take them down themselves. worst they can do is say no.
garage sales, flea markets, businesses, friends, and trashbins and local dump sites are al valid places to find authintic coolstuff.
if none of these options do it for you then the only option is to try to buy all new stuff.
just my humble opinion but all new is hardly ever really cool with the wow factor. it usually takes time and a little effort to achieve an atmosphere of cool that represents all the interests of a collector of cool stuff.
cheers
