Ebay should be your best bet in this day and age. Just search for resin model kits basically. Avoid everything out of Thailand unless you're a masochist or they are original sculpts by Narin sold by him or it will still be recasts. Seriously, even if you don't care about the ethics of recasts and all that - the quality just plain sucks and so do the materials. There are some awesome sculpts out of Hong Kong, but most stuff coming from China and HK are anime recasts. There will be some studios that do original mecha and stuff, but you just really have to research according to interests. Kickstarter can sometimes yield good results, but there just aren't that many "figure kit" news outlets really. Miniatures are much easier. Much of the hobby was simply taken over by sideshow and other ready painted collectibles when it comes to large scale figures.
If you want to research what is available "the clubhouse" used to be a goto forum for figure kits that catered to western popular culture. Buc wheat used to collect news for figures and archive old news. "Monsters in Motion" still has a lot of kits I think. Still - trawling ebay is your best bet for old stuff (and some new). Unfortunately I don't know many sites that are strictly "garage figure kits", it's more like finding forums that have sections that figures are a part of. Other than that there is the "resin kits" subreddit, but it's very anime centric. There is garagekitsuscolors.com that have some stuff. You should check out some channels on youtube to get some hints of what is currently produced and where to get it. Rafael Robledo jr is one and the other is Vince Vell customs.
I would recommend simply getting a 3D printer and joining the "printedminis" and "3d printing" subreddit and then joining the patreons of sculptors you like. You will drown in kits of very high quality. You can also find tons of free stuff on Myminifactory (search for printed obsession and Eastman). There is a learning curve, but you can basically buy a resin printer for the price of 2 medium priced resin garage kits. I have more choice than I could finish in a lifetime it seems. Checking out what is out there is free anyway.
