there's a list of eurorack shops world wide in the stickies of the eurorack forum on modwiggler.com
it's not 100% complete, but it's pretty good
"some of the best base-level info to remember can be found in Jim's sigfile" @Lugia
Utility modules are the dull polish that makes the shiny modules actually shine!!!
sound sources < sound modifiers < modulation sources < utilities
Sweetwater's modular selection is actually fairly slim when compared with dedicated USA shops like Noisebug, Perfect Circuit, et al. They're good for those situations when you need some basic module(s) NOW, though.
My favorite to work with so far has been Patchwerks...those guys have gone above and beyond for me a couple times. Also have had good luck with Detroit Modular, Analogue Haven. and Perfect Circuit.
It is the one that has in stock the product you are looking for and that you did not find anywhere else.
My own best memories are: Signal Sounds (wonderful Jason), Escape From Noise, and Modularsquare... :)
'On ne devrait jamais quitter Montauban' (Fernand Naudin).
I'm in the US and mainly use Patchwerks (Seattle-based) and Perfect Circuit. Patchwerks I find has a solid selection and great recommendations, service, and ship times. Perfect Circuit has a wider selection. On rare occassion I've bought from Detroit Modular and a shop in Oregon who's name I forget. All 4 of those have been worth going back to.
I buy most of my other stuff from Sweetwater, or less frequently, Vintage Audio King, but both SW and VK are much less knowledgeable in modular than those specialist retailers mentioned above. Hope this helps!
One other point regarding both Reverb and eBay these days: I'm seeing prices drifting upward, so both places might be a good source for outboard effects for a while longer...but certainly not forever!
I’m pretty much all reverb and ebay and paying anywhere between 50% - 70% of rrp. The only module I bought close to rrp recently was metropolix. Just got to walk away if the bidding gets too high than what you are prepared to pay.
My standard search has become Reverb/Ebay, then Perfect Circuit, Patchwerks, then "well who's got it in stock?"!
Edit: oh, and buying from makers directly where possible is early in that list too!
In the USA,
Detroit Modular has been my go-to place for most things.
Perfect Circuit is second. Their shipping can be a little slow.
After that, I just hunt around. For most modules, there aren't any big runs on product. So finding a lesser known brand of module usually leads me to whatever online store has a unit rather than me giving deferential priority to a specific vendor.
Here in the US, Patchwerks has become my favorite, with a tie between Control, Control Voltage, and Detroit Modular after that. Also one source I haven't seen mentioned yet is Juno in the UK. They don't have the widest selection but their prices tend to be pretty good on the whole. Unless there is some reason not to support them that I am unaware of, they can be a good option depending on the manufacturer you are looking for.
I go to Reverb first to see if there might be a reasonable deal on a used module, but do the math - the asking price can sometimes be close enough to retail that when adding tax and shipping (sometimes outrageous shipping), it is just as much if not more than retail from say Patchwerks, which includes free shipping and zero sales tax. I wish I could buy more from Midwest Modular, but since they’re local (Minnesota) they have to charge me sales tax. Patchwerks is great. Perfect Circuit is great. Detroit Modular is my favorite because they have a loyalty points system, and that is totally great. Mostly, I tend to surf them all to see 1) who has it and 2) is there a lower price between them. If the price is the same everywhere, I’ll buy from Detroit Modular to rack up a few more points. Ah, consumerism.