I would definitely offer to buy them since you are asking for quite a few of them. They pay for them just like everything else they stock, so I don't see why they wouldn't sell them to you for a reasonable price. If you're shipping livestock, I would even ask if you could bag with their oxygen (as long as you're not undercutting them in any way). Most LFS, especially if you're a regular customer, should be willing to work something out with you.