I looked for one as well when I had my Allround but had no success finding a factory magwell. These don't seem to be stocked as accessories so perhaps they need to be ordered as replacement parts. You could try the Canadian distributor, MD Charlton, to see if they have any or if they can get them (don't know to what degree the German Sig export ban applies to non-restricted parts).
You may be stuck going through a European dealer. If that is the case, you could call Markus at the Calgary Shooting Centre and he might be able to source one more easily.
It is well worth trying to get one. It makes for a much better grip feel for me.
Alternately, some companies make/have made them or variations of them:
http://www.rocosystem.com/competition-gun-accessories/
http://www.trt-tac.com/Magwells_c2.htm
Another option it to get the Nill grips with the integrated magwell. That would be the next best thing. I'm not a fan of the Hogue equivalents on the Tacops model but that is another option.