Here are some of my sources. I apologize in advance if there are duplicates:
Do-all suppliers (these carry more than one type of item):
www.usaknifemaker.c omwww.sportsmansguide .comwww.amazon.comwww.etsy.com (yes, I also have an Etsy storefront, it's a good way to find not only used vintage gear but also handcrafted items like most hobbyists make!)
Buckles, cordlocks, fabric, webbing assembly etc:
www.diytactical.comwww.cdwplus.comwww.itwnexus.com/Raw materials:
www.grainger.com (barstock, sheet metal, fasteners of all sorts)
www.riogrande.com (jewelry making supplier, carries all sorts of precious and semiprecious metals and minerals in raw form as well as various types of fasteners and tools for such endeavors)
Leather/leatherwork specific suppliers:
www.tandy.com (I almost never order from them due to their fairly high prices, hard to find local stores and hard to navigate website).
www.brettunsvillage .com (this one I was reluctant to share, but since you guys are all pals here I figured "why not" lol. They're a best-kept secret amongst hobbyists, haha).
Free/scrap material local social sources:
www.craigslist.comwww.freecycle.org (although I haven't had any luck being added to the lists as far as I know, they seem pretty discriminatory in my area, not sure why!)
Tools:
www.leevalley.com (good tools, kinda expensive but some are worth it)
www.garrettwade.com (also good tools, not too bad pricewise usually)
www.harborfreight.c om (my el-cheapo belt sanders are still going strong, three years later!)
www.grizzlytools.co m (better tools in some cases, not much more expensive).
www.ebay.com (score lots of good hand tools this way if you've got the knack of search-fu)
Gun related sites:
www.sportsmansguide .com (ammo, parts kits, gunsmithing tools, and other stuff)
www.cheaperthandirt .com (ammo, parts kits, assembled guns, gunsmithing tools, tac gear, knives, prepping stuff, and other stuff)
www.midwayusa.com (ammo, guns, gunsmithing, parts, nearly anything gun related)
www.natchezshooters supply.com (almost identical to midwayusa in terms of content, with perhaps slightly less inventory)
www.brownells.com (gunsmithing supply. Almost anything you need for gunsmithing supplies you can find here)
www.e-gunparts.com (huge ass site chock full 'o' parts. The stuff listed isn't even half of what they have, most likely. Call them or email for details).
www.gunblast.com (reviews, etc)
www.youtube.com (obviously! Lots of tutorials on everything gun related, field strip, detail strip, reviews, ammo tests, how to, etc etc)
www.celticarmory.co m (tutorials on detail stripping, I found his Browning Hi Power video very helpful!).
http://world.guns.ru/main-e.htm (reference site)
https://en.wikipedia.org/wiki/List_of_firearms (reference site for all small arms including military stuff)
And of course, never underestimate the power of personal, day-to-day networking with family, friends, coworkers and random people you meet, haha!
PMZ