I have two genuine Colt 10-round magazines with the 20-round bodies. These pre-ban magazines were included with pre-1994 Sporters, as I recall, but after the ban, Colt changed their design, because people were drilling out the rivet in the bottom plate and converting the magazines. (I emphatically recommend against doing so!) I'm selling these magazines, because I just don't need them.
Price is $20.00 each. MO preferred, PayPal accepted with 3% additional charge. Shipping is $5.00. IM me or drop me a line at firstname.lastname@example.org