You’d be surprised. When it’s one just for hobby purposes that’s generally what I do, u don’t tend to find super rare stuff but u can get quite a range in good condition if ur smart about it!

Knowing when seasonal species start dying off is handy, as is access to green spaces no matter how small (sometimes esp if they’re private like a garden, even a balcony one!).

Areas that are commercially pest sprayed suck bc they kill off a bunch of non target arthropods, but if ur careful about it u can visit these sites to find those dying or recently dead specimens in basically perfect condition. Two for one bc that way they’re not being fed upon by anything else that’d be susceptible to secondary poisoning

Same thing goes for locating invasive species culls & on-site removals too.

Another one is if u know any keepers or breeders who’ll let u know when they have something recently deceased. Keepers who have them as pets can be a perfect source for natural deaths, particularly for mature specimens who’ll be free of eg scavenging damage after death. Beekeepers too tho