I would start with the dealer you purchased from. They should be able to offer a lift which works with your spa siding and cover.
If that doesn't work, go to "rhtubs.com" and select from their many offerings. That site is operated by one of the frequent posters here on this forum (not me) and I think they offer free shipping in certain cases.
Most of all, you want a lift which doesn't hold the cover by the hings. Even if you buy a lift which DOES that, you can add a strap kit which transfers the weight of the cover to the bottom - see Robert's site for more info about that.
HTH
