Can't help with where to get one but I can say they are worth it. When we had our Cub it had one and they certainly make a difference. Camper didn't get as hot, didn't get condensation on the roof when cold, and it's also quieter when it rains. They also catch all the bird sh1t which means it's a simple job to take the tropical roof off to clean rather than having to clean the roof of the camper. A little more time to put up & take down but not much.
The only things I didn't like about them was that:
- it was difficult to find the balance of how much to tighten them. If you tighten the tropical roof as much as it looked like it needed to keep it quite taught then it had the effect of pulling the camper boxes down which made the side walls of the tent slacken off, particularly at the front.
- because the flexible bows that support the tropical roof are curved when under tension and higher in the middle, the strap for the winch always slid off one side and had to lift back onto the roof to close the camper.
On balance definitely worth having one though. Cub's price may not seem exactly cheap but I still think I'd rather get one from them. That way you know it's the right shape & size and if you have any issues with it, or with the camper when it's fitted, then you can go straight back to them. Also remember that as well as the canvas and the 3 support poles you'll also need the tethering arm that fits under the back of the camper floor and you tie the back of the tropical roof to it.