Probably have to look at refurbished laptops then. Ebay, Newegg be good places to look. You can widen your search by not looking for ones with SSDs already installed, you can swap out a regular HDD for a SSD easily on your own.
Biggest problem you'll have is since you can upgrade W7 to W10 for free most refurbs have already done that.
You can always run W10 and install a VM running W7 so you can run your proprietary software. I did that for years to keep a program that would only run as high as Windows XP going for years. Actually still going right now, we only just now finalized a contract to transition to a replacement program.