The regular grocery stores in SoCal care Portuguese linguiça which is very similar to Spanish chorizo. I like to make paella on the BBQ, but I have no good advice for the bomba rice.
This is what I use also - Portuguese linguica instead of Spanish chorizo. When I lived on the east coast, I could get the Spanish chorizo - but here in San Diego all chorizo is Mexican style - and it is NOT good in paella.
(That said - DH discovered if he uses a little pork chorizo (Mexican style) in his lasagna red sauce - it tastes really nice... he claims it is "what Lasagna has been missing". He's 100% Italian and learned how to make lasagna from his Sicilian grandmothers... so he's allowed to make statements like that - and his lasagna is VERY tasty.)