for some reason i think this question was asked before but here it is again.

do you look at the official label site or something other discography/catalog site and hope that the (OOP) is listed next to the title, or is there some other resource?

yes, that is one of the best ways. most bands will also make a note of OOP releases on their website's discography. but if it's for a band without a site, one way to find out may be checking ebay to see if it's up there and listed as OOP. although, it's definitely possible that they are bluffing. there is a record store in town that marks a certain multi-disc album as OOP and marks up the price, but it's not.

Other than checking the label site, I general gauge this by looking for something at Half.com, Amazon, and Gemm. If it's really scarce and expensive at all of those places, I generally assume it's OOP.

For instance, I've been wanting to get James Chance & the Contortions - Buy for a long time, but the only copies I can find through any reliable sources are over $18. I've never seen it in any stores, and hardly anyone online (that I would trust) claims to have it. Pretty safe to say that it's currently OOP although I could be wrong.

they also just repressed buy a couple years ago on really sturdy vinyl (like 210g, or something), so that's keeping prices of that one up too.

Yeah, I saw the vinyl in Full Moon Records a while back, and I've been kicking myself for not picking it up (it's gone now). It actually wasn't too expensive as I recall.

I was gonna recommed Amazon. If it's only available via an "Amazon Seller", & not the mothership itself, chances are it's OOP.