I did a little research on the MecGar mags - there is one seller out there claiming to have MecGar mags for 4006, but if you check MecGar's site, they only show for 5906. As was pointed out the 5906 mags will most likely fit into the magwell but MecGar lists no mags compatible with the 4006.
There were also some noname mags out there a few years ago that claimed to work for both 5906 (15rd) and 4006 (11 or maybe even 12 rd) - I think I have a couple but I did not find them of sufficient quality to trust.
iBuyItRight on GB had factory SW 10 rd 40SW mags at one time - not sure if he has any left, but might be worth checking his current ads for 11 rd mags and messaging him. I bought CHP 4006TSW and extra mags from him a few years back when he had several listed - back when they were going under $500 - and he was always good in responding and good to deal with. You might get lucky.