http://www.bcsgrammarandtextbook.org/ You can get it through Amazon. :)

Oh ... yes.... you can still get Serbo-Croat at Amazon.

I think the old book, Serbo-Croat by Vera Javarek and Miroslava Sudjic, is the best for learning the grammar. At this Web site at Indiana University there are lots of exercises: http://www.iu.edu/~celtie/serb_croat_bosnian_archive.html Bosnian for Foreigners is the absolute best linguistically but very difficult.

I've been using this book for the last couple of years. It's rather technical and not entirely pedagogically sound, but for my style of learning it's been very helpful. http://www.amazon.ca/Bosnian-Croatian-Serbian-Grammar-Sociolinguistic/dp/0299211940/ref=sr_1_2?ie=UTF8&qid=1389745472&sr=8-2&keywords=ronelle+alexander