The purple Stick is the model 3500. The new remotes will not work on it. Roku no longer offers a compatible remote for the 3500. Since no Stick supports IR, you only have two options: find a used remote on eBay, and hopefully the seller is honest about it being a 3500 remote, or buy a new streaming player. Considering the prices I've seen for used remotes, I think you're far better off with a new player. If you get a new Roku, either the Premiere or Streaming Stick+ are good choices. If you don't mind the Amazon-centric user interface, the Fire TV is another choice in the same price range.
And yes, the 3500 is no longer supported. It's not powerful enough to run many of the latest channels, such as Disney+.
Dan Ultra (4640), Ultra (4670), Ultra (4800), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.
We no longer offer a replacement remote for the Roku Streaming Stick model 3500. However, we would be happy to see what we can do to help get you back up and running.
Please feel free to send me a PM with your Roku account email address and the serial number of your Roku device (printed on the side/back of the device) and I'll have our support team reach out directly to assist you further. Meanwhile you can use the free Roku mobile app as a replacement remote control.