Need help finding buffer to mpx adapter or similar

[new shooter]

Hello everyone!

So I have a mini project and my google is too convoluted with stuff I don't need.

I have a sig sauer swat 556 pistol that is like to add a mpx brace on. .

The swat uses a regular ar buffer threaded hole like this picture below(that photo has a cap over it)



The mpx pistol utilizes a picatunny rail for their stock or brace attachments pictured below...



My goal is to somehow get a picatinny attachment on the buffer area so that I could mount mpx style brace to a standard AR buffer tower.

The brace I want to use on my swat is shown at the link below.

http://www.opticsplanet.com/sb-tactical-mpx-pistol-stabilizing-brace.html

Any help would be appreciated. Thanks

[new shooter]

Something like this but with a brace instead of a stock would be ideal!