New discs are now available at league night which takes place every Wednesday at 5:30pm. Email info(at)grenadodiscgolf.com for more information. Another option is Fallow Ridge in Coldstream (just east of Vernon). The owner of this private course has a good selection and fair pricing. You'll certainly want to check out his creative course while you're up there. It's about a 1 hour drive from Kelowna. I believe you can find 3 packs of beginner discs at Canadian Tire and Sport Check but these likely won't be suitable for anyone who's serious about playing. Other options would be Kamloops and Vancouver.
The Knox Mountain course doesn't have any drinking water so you may want to pop into the convenience store just a few blocks south on Ellis. It's the closest store of it's kind. Afountain is sometimes operational in Sutherland Park immediately south of Knox Mountain Park.
Knox Mountain Park Development Plan - Info on the new 10 year management plan
British Columbia Disc Sport Society - Courses, Tournaments, Tips and More
Professional Disc Golf Association - About, Courses, FAQ, Videoand more
Calculating Your Disc Golf Handicap
Youtube: Disc Golf Introduction
Youtube: Long Drives Tips/Techniques
Youtube: Putting Tips/Techniques
Kelowna Ultimate Frisbee League