I have been looking for spare mag for this weapon. What other models share the same magazines? Does the P228 or 229 fit it?  Thanks.

15 and 17 round mags marked P229-1 are what you seek.

My mecgar 17rd ones work great!  They are p229-1 also.

On the M11-A1, any of the 9mm P228 or P229 mags will work. The M11-A1 uses the 40S&W P229 frame that sig standardized on in the early 2010's. So you can use the 13 and 15rnd P228 mags as well as the 13/15/17 rnd P229 mags.

^^^This but with one issue. The original 228/229 mags will have some wobble to them when inserted into the mag well. The 229-1 mags will not wobble in the mag well. Whether it will cause issues when shooting them or if you ccw the weapon, increases the chances of something going wrong. They will all lock into place but it is possible it can cause issues. I prefer to use the correct mags for the gun. It's a shame they all can't use the same mags without issue but Sig likes to stir things up.

I've used P228 and older P229 mags in a newer P229 SAS Gen 2. The size of the mag body isn't drastically different, so there is not as much play as you would expect.