Short answer: NO, there are quite a lot of pre-built wheels made for use on older bikes (or new ones) that come set up for a freewheel rather than a cassette. There is a US based company called Wheel Master that most shops can get. I see you're in Canada but I still think you should be able to get them from a shop.
I would not suggest trying to rebuild your wheel unless you are comfortable doing so as getting the spoke tension and everything dished correctly can be difficult if it's your first time.
I will provide a part number for reference, again this is a US based company but they ship to CA as well as a lot of online retailers. If I had to guess this wheel wouldn't cost more than $40 US currency plus a new freewheel if you want one. Point being they are out there, as that was your original question.
However if you want change rims only that would be a viable option, although if you're on a budget having both redone could be almost as expensive as two ready made wheels, depending on labor costs etc
If you go the pre-built route double check the spacing first as the O.L.D. has changed some over the years.