Seefut,
In general most manufacturers do not produce a rectangular spa. However, there are two spas that Hotspring manufactures that are rectangular and going by your measurements would come close to fitting in your space. The first is the 6 person with lounge Sovereign that is 6’8’’ X 7’9” and the second is the 5 person with no lounge Prodigy that is 6’2” X 7’3.” The Sovereign is a much more popular spa than the Prodigy. I would guess the Sovereign will cost in the $7,000 to $7,500 range and the Prodigy in the $6,000 to $7,000 range.
I hope this helps and ask away if you have any more questions.
Chris H