Can we upgrade PowerPC Macs to OS X 10.7 now that 10.8 is out?
If your attempting to upgrade a PowerPC Mac the most you can upgrade one of those is Mac OS X 10.5 Leopard, since it was the last version of OS X to support PowerPC processors.

So the answer is no to upgrading to any OS beyond Mac OS X 10.5 if the Mac your trying to upgrade is has a PowerPC processor.

If you have an Intel Mac that support OS X Lion and you really want Lion or if Lion is the last version of OS X that your Mac can run, you will be able to contact Apple and arrange a way to purchase it via Apple's legacy products list as noted in the following MacWorld article: Apple pulls Lion from the Mac App Store


  ...while Lion is no longer available for sale from the Mac App Store, customers can still purchase it from the legacy products list via Apple phone sales.


So if you really want lion contact Apple at 1-800-MY-APPLE and let them know you want to order OS X Lion.