Is there still a way to purchase Sound Forge Pro 10?

Not from Sony or Magix. Someone on eBay or elsewhere may want to sell SF-10. If you can find it, make sure it has a valid serial and Magix log-in info so it can be activated, or have the seller change the email address prior.
FYI, SF-10 was the last version that had the legacy non-modal Fx chainer and 'record' UI. It does not support VST-3 or 64 bit plug-ins. SFP-10 included iZotope's Direct X Mastering Suite II, which you may or may not be able to activate these days. iZ's DX mastering suite II had some really nice (UI and sound) multi-band plug-ins (Comp, Exciter & Imager).