www.coolgunsite.com and www.M1911.org have good info on genuine USGI and Colt magazines. Avoid magazine with 30745 code on the bottom; most are fakes. Those with 1M291 on the bottom are made by Checkmate and are legitimate USGI surplus.
Study the reference material. Depending on the SN#, 1913 Colt should have early keyhole or later lanyard loop mags. If you are lucky with SN# less than approx 30000, it will cost you a fortune to find keyhole mag (expect $400-$500 each). For later 2 tone lanyard loop mag, you can still find those on eBay for $75-$150 depending on condition.
Here's the old 1911, serial 59XXX. Has a lanyard loop on the foot of the grip. Mag doesn't have a keyhole or any other markings. If anyone has comments about where to get OEM mags for it, I'd appreciate it.
Most Colt items in good+ condition (made before 1970s) carries a premium price and continue to rise. Your 1913 Colt is in good condition and deserve a period correct mag. Cry once and you will be happy.
Not a straight comparison to your situation, but I am seeing all pre-WWI lanyard loop mags climb up in price. I had 1913 Colt SN#28xxx and cost me $300+ to bought extra keyhole magazine in very good condition years ago. Nowadays to find one will cost me $500+. Look at what I just found out on eBay. That one is below average condition. Colt “Key-hole” 1911 cal. 45acp type 2 Punch-and-saw magazine | eBay
But the lanyard loop is on the gun, not on the clip.
Also, I have the original clip that came with the gun. It's just not in the pic. Just looking to pick up a spare. Everything on that gun is original - the grips, the screws for the grips, and the clip. It's all there. Thanks for the valuable information.