[Will Day]

Admittedly, unless your apple vendor is willing to offer full-credit, it would be a hassle to trade it/sell it and get a macbook known for sure to work with 10.8. Contact the software maker for an ETA on when it might work with 10.9.

If you are going to wait for the software update, and have a few hours to burn, you could actually try this:

1. Disk Utility > Partition > shrink the 10.9 boot-volume (probably “Macintosh HD” to free up maybe half the disk, or at least say 40-60gig.

2. After shrinking, hit (+) to add a second empty volume, and name it “108tobe”.

3. Do a clean install of 10.8 onto the “108tobe” volume, leaving the 10.9 volume untouched.

4. Try booting 10.8 by holding down the option key during power up to choose whether to boot 10.8 or 10.9. To keep things sane, when using 10.8 un-mount the 10.9 volume, and vice-versa, using Disk Utility.

If 10.8 runs at all, or at least well enough to use, you could stick with that until the software runs in 10.9. You’ll quickly see if the missing drivers are major items, like video or 802.11ac wifi, then 10.8 may not run well enough to use.

If the software runs on windows, then maybe boot-camp to windows instead of 10.8. Ugly though.

PlainVanilla

[Will Day]

If the new mac came with 10.9, it may (or may not) have hardware that requires drivers not in 10.8. If you post the model number, we might be able to tell whether 10.8 would work or not before you investing the time trying only to find out it is a no go.

A quicker safer alternative to get a mac that runs 10.8 is to take your new 10.9 mac back to the Apple Store, and ask if you can return for full credit towards a macbook-pro that will run 10.8, such as refurbished one from Apple on-line:
https://store.apple.com/us/browse/home/specialdeals/mac

The refurbs from apple come with same warranty as a new one. I would not bother with applecare, but if you already paid for it, ask that it be transfered as well.