I have a Briley F13 Fantom in 40 cal. Does anyone know where I can buy magazines for it or if another kind will work with it?

Caspian.  It's a Caspian frame.  Please don't kill the messenger when you see the price.  Also, call them, as they don't list the shorter mags on the site, and they might be a special order type of situation.

ETA:  Now that I check their site, which I have not done in weeks, I can't find any of the hi-cap mags.  If memory serves, they are $89.95 apiece.  Regardless, call Caspian or shoot them an e-mail, and I'm sure they will take care of you.  They have stellar customer service.  Also, I'll be making an order later today, so I can ask them about the mags.

Thanks alot for taking time to share information with me.  I'll check and if you don't mind when you talk to them let me know. Thanks Again!

Found a  few through Briley. $55.00 a piece. Not cheap.

Jump on them, they cost $89.95 from Caspian when they had them.  I was about to call the other day to make an order, but it seems I qualify for a discount, to I'm holding off until I get an e-mail from them.  I'll let you know what they say about the mags.

Thanks, if the discount is enough maybe we can get some. They told me they didn't have any.