I doubt you'd persuade SM to let you have a new installer. A friend of mine's Poser 7 disk developed a fault and he couldn't get a replacement, so now he uses DAZ|Studio...

If you're willing to pay, I'd think that unregistered physical copies of P7 would crop up on eBay, or the software surplus sites, from time to time. They shouldn't cost too much. I think I paid $39.95 for mine, so I'd regard anything more than that as a rip-off.

Do take care to check that it's from a legitimate source, of course. As far as I can remember, you aren't allowed to transfer ownership of a Poser licence.