You probably want to pick up the trumper's sample pack if they do that - you get to sample their skin foods.
My ideal aftershave has no scent so that I can just use fragrance as I see fit, but I don't think I've found that one yet. The stuff that I usually use is, it's not in-your-face but stays for a bit
coral skin food - an ok rose, which stays for about 1/2-1 hour on me
pre de provence - it's a balm that is quite herbaceous but i like it and don't mind the scent staying for few hours
penhaligon's lords asb - also stays for few hours, but i don't mind
alt innsbruck the lotion version - pure tobacco scent same thing few hours
yardley original - a bit dated for my taste, but it's good and stays all day, you have to find it on ebay
i also use czech&speake 88 aftershave and it's really really strong which for me isn't very desirable. i pretty much use it as I would a strong cologne.
as far as fragrance samples there is a guy rorschuck on b&b who provides decanting service at really attractive prices. there are of course few places on the internet that do this. it's really more for fragrances and not aftershaves though. I think a lot of vendors would add samples to your order too. sometimes I've mailed people samples, but I don't have the time or interest to make anything formal out of it, plus I'm trying to limit my stuff, not expand it :)
The best way I can see something like this happen is to have one person who is interested in providing decants. I've seen few cases when people start a travelling box where at each stop you can check out the content, replace few things and send it on, but they always seem to end up badly.