I am considering purchasing a new P210 for casual IDPA. But I will need 3-4 mags to compete. Are the P210 magazine body the same as a P239 or P225A1? I just made three P239 9-round magazines. I found new P225A1 magazines and jumped on them. Then I ordered plus one extensions from Galloway. (Note. 9mm and 40 are different). The new extended mags work perfectly. So, will these fit the P210 standard pistols? Thanks for any responses.

I had the same problem for my P210A Standard. Other Sig mags (P225A-1, P239) did not fit. The cheap solution was to buy mags for P210A Target (having huge baseplate) and then swap the baseplates with P225 baseplates, which fit perfectly. Numrich used to have them.
The resulting mags stick out of the bottom of the grip just a bit, but this is easily remedied with a rubber band and they look classy. So the key was to find P210A Target mags for cheap-I got 3 used for $20 each.

On the above note, there was recently a thread where somebody put 239 +1 bases on 210A mags and they worked as intended.

Top Gun Supply has these magazines in stock.
These fit the p210 legend and p210A standard.

https://www.topgunsupply.com/s...mm-8rd-magazine.html

I used galloway +1 extensions for the 239 on three P210 mags. This is the thread:

https://sigforum.com/eve/forums...140006664#6140006664

I also bought several target mags and swapped out floorplates. This one worked the best, for me:
https://www.midwayusa.com/prod...006093088?pid=196246
Using this plate to lock it in place:
https://www.midwayusa.com/prod...006099179?pid=949393

They cost me nothing because I already had lots of mag parts for S&W single stack mags.
They look perfect on the P210 American. (In my opinion)
I am working on a ten-round magazine using the aforementioned +1 galloway base and trimming some of the follower to allow another round in there. I think four or five 10-round mags plus six 8-round mags will be the “right” number.
If you call the Sig Pro Shop in NH they sell the 210 Legend mag over the phone for $39. Its the same magazine.

Walther P-38 mags are another possible source for mag conversions. They are almost exactly the same as P225 mags and cheap.

Is this them?

https://sigsauerguns.com/sig-s...mm-8rd-magazine.html

Yes. Thats the mag. But the pro shop is this:
https://www.sigsaueracademy.com/facility/pro-shop
Either way thats the best price I have seen. I bought a dozen or so at that price and was pretty happy.