Many of the generic drugs made by Sun and Intas are made only in the XR form, although they don’t have XR in the name. I don’t know about the two above, but it is the case with Effexor which I take.
The non time release Seroquel is $16 for 60 tablets of quetiapine 25mg (generic) at Walmart with the type of coupon I use (GoodRx). Very unusual for more frequent administration of the non-XR to not “work”.
I found this:
http://schizophrenia.emedtv.com/seroquel-xr/generic-seroquel-xr.html
“Although the patent for Seroquel XR (quetiapine XR) is not set to expire until May 2017, a generic version may come to market sooner than that, due to the result of a legal settlement. Until a generic becomes available, keep in mind that while some companies may claim to sell a generic Seroquel XR, these drugs may be fake, substandard, and potentially dangerous.”