I always wanted to add a sig P239 to my collection and when the opportunity presented itself I bought a used P239 in 9 mm couple weeks ago for a very good price, only to find out that sig has discontinued this model and there are no magazines for P239 of whatsoever. The gun came with two magazines, but I usually like to have at least 4 or 5 mags per gun for practice, range use, etc.. My happy feeling about how the P239 handled at the range was washed out quickly when I searched online for extra mags. There are some used mags on eBay that are selling In excess of $100. And people are bidding on them in an endless bidding war.
I did some research and noticed that the new sig P225-A1 has a similar shape magazine as the P239 but with a different base plate. So by judging from the pictures I ordered two p225-A1 magazines for $33 each. They came in two days ago and my guess was 100% right. The steel body of the magazines are exactly the same as you can see in the pictures.. I think Sig just took the P239 magazines and made a new crappy plate to fit the new model P225A1. They were not even innovative as they could have designed the base plate for the P225A1 to hold an extra rd. Any ways, as is the mags load and function 100%. I haven't shot them yet but the slide locks fine.
The plan is to just keep them as is and use them in the P239. If I decided later that I'm bothered by the fact that they don't fit flushed, I may buy a stock P239 plate running for around $12 on ebay or get the plus 1 by Galloway for the P239. Just wanted to share this tip with the P239 9mm owners. Unfortunately the P225A1 does not come in 40 or 357 Sig, but apparently these magazines for the P239 are still available for reasonable prices on the interwebs..