if its running Win 10 just use the MSFT  Media creation tool to create a USB install media and use that. Windows will deal with the drivers and the install will activate as it is recorded to the store with the PC's ID.

HP are the reputable source to get restore DVDs from , if they were available at all.
Given just how old it is, dont hold your breath (circa 2012)

Service techs etc would just use a generic WIn7 DVD, then install drivers manually. So I wouldnt trust any overseas selling restore DVD's . God knows what would actually be
on it
The other option is to download & install Win10. Use the Win7 install key on the attached COA sticker

Thanks everyone for replies and suggestions

Keen to stick with Windows 7, so will try first to use restore CD for different model.

Failing that, call HP and try and get free given how old this is