Would this work for you?
If your tub drain kit is 1-1/2", there's no harm in using a reducing coupling to bring it up to 2" before it meets with the 3". That way at least you wouldn't have to wait for a UPS delivery.
(BTW - I've never shopped at either of the above sites before, so can't comment on whether you should use them).
Could I just go with a 2" Drain line for my tub
It can't hurt to go 1/2" bigger if your drain kit can connect directly to 2".