ORM-D shipping of ammunition will probably make small quantities of ammunition cost prohibitive. You'll probably get a better deal through online sales. I can get it locally for about $65 a box with tax, when I was looking for some. I managed to 100 pieces of brass, so it'll be this winter project to develop a load.
This is the ammo that is available for $65 locally it's $15 cheaper at Grab A Gun:
Winchester Deer Season XPAmmoseek.com has a few
options for you in .270 WSM. I know this isn't really what you asked for, but properly shipping a 20-40 rounds of ammunition will run you over $4 per round for the average guy at UPS or FedEx.