Grey Ghost Games publishes A Magical Medley for Fudge, which has several magic systems detailed. Given that it's Fudge, which is basically "build your own game", conversion shouldn't be too difficult.
My favorite is "Occultism", inspired by Call of Cthulhu and ritual magic in general. BRP already has a "Sixth Sense" (POW) stat, an Occultism skill, and a Sanity system, which is all you really need.
EDIT: To answer your question more directly, you can find Avalon Hill's RuneQuest 3 materials on eBay and used games sites. Despite the publisher, RQ3 is essentially Chaosium's RQ system revised and expanded. The "Sorcery" system is essentially an expansion of BRP's Magic rules, and some "Spirit Magic" or "Divine Magic" spells might work in BRP's Sorcery.
Last edited by fmitchell; November 19th, 2008 at 17:38.
Frank
"There's something that doesn't make sense. Let's go and poke it with a stick." -- The Doctor, Doctor Who, "Amy's Choice"