From time to time .356TSW ammo appears on Gunbroker for sale. I don't think Starline is still manufacturing the .356TSW cases. Not sure if any other cases can be used
Looks like one of the pistols shooting .356 is missing-the S&W Super 9-another rare offering by S&W primarily targeted at the European IPSC shooters with a few pistols left for US shooters. I was able to buy one from another collector. Anyway the pistol came with 3 barrels: 1) 9mm; 2) 9x21...
A second disadvantage would be the rounds available to you in the Shield. The Shield would normally qualify as a BUG in IDPA. But shoot it and have fun.