These filters are availsable from
Speciality Pool Products. I have purchased several items from this company and always had great results. I did a little more research and found that this hot tub is manufactured by Icon Spas. If you select Icon Spas for you OEM it will brin up a list of cartridges (filters) that they used. If yours is like mine it is the:
Filbur# FC-3077 Pleatco# PWW 10 Unicel# C-4310 SPP# ZCT3077
Desc: 10 sq. ft. Skim Filter, Waterway Skim Filter 10
Outside Diameter: 4 1/4"
Length: 4"

Their cost is about $10 each (slightly less if you order 2 - and my tub takes 2). They do not charge shipping but do always charge $8.95 handling no matter what you order...

Good Luck.