I second Wearing Clouds (when they go back to shipping out orders that is) it is a very convenient service at a fair price with a wide selection of diapers (even some that may be hard/expensive to get in The United States) ; I did a sample order with them and received it in a few days.
Wearing clouds is a good place to find some samples, but there are eBay listings for cheaper. Wearing clouds is only a sample of 1 diaper, which doesn’t really give you a good enough sampling to try out. eBay listings I find usually sell in samples of 2 and they are cheaper per diaper usually when compared to wearing clouds.
Abdl factory has a large sample pack of ~35 abdl diapers for about 70 bucks (two bucks a dip)(might be ~80 in usd) but I’ve had more experience with wearing clouds personally cause of there focus more on Abdl diapers than abdlfactory which has about as many diapers as you could image but didn’t have to one I wanted at the time(pride diapers)
Edit: was wrong about pricing and number but it’s close enough.
I always just check out the reviews and then order a case .
The only place I have ordered from has been Northhore and they always send me some kind of diaper samples .
I have been thinking of requesting a sample of thair mega Max and supreme lites .
I only order about a case a year as I don't tend to wear to often .