I own a Sig226R SS that shoots both and I "have" both barrels. You can get the brass off Ebay and I think Marstar has some as well. I got my Honaday dies from Gobles in London. Just to let you know, because this is a "necked" casing, you can't get them in carbide, so the casings must be lubed before sizing. Also, look up the reloading data on the net, as there is only one or two bullets that are any good for reloading, and they are both hollow point, if memory serves me right...
PS: As I understand it, you can't resize the 40S&W for the 357Sig, as the 40 case is not long enough after sizing...
Cheers
Dean