Quick search turned up some stuff that may be useful.
14 round mag
http://www.promagindustries.com/product-p/hip-a4.htm
forum search turned this up
http://www.hipointfirearmsforums.com/entries/High-Cap-Hi-Point-Mags.html
Pro mag has a 14 round magazine for it. Quality seems to be spotty...
Item for sale/trade: Hi Point .45 ACP Carbine *******SOLD 03/02/13********
Location: Pensacola
Price: $500.00 or trade for a nice XDS/XD compact .45 or the like
Gun is in 'Like New' condition with only 1 box of rounds fired through it and cleaned after use.
No issues, lockups, or problems of...