Yes, in that case your probably better off buying something that is more easily matched up.
I think 8 speed Shimano is backwardly compatable with all 5 / 6 / 7 / 8 speed Shimano stuff, both mtb and road. If the shifters have more 'speeds' than your cassette, then you just ignore the unused 'clicks at the end of the range.
Hunting on
eBay for this sort of stuff might be the way to go. Don't discount bar end shifters if you find some. 8 Speed barends were 'ultegra' quality and should be servicable for ages.
Eight speed STi levers were also still available new till last year and many shops will still have them in stock (NOS). They were the SORA model.