ebay has a few copies, this is one I just found after a brief search:
https://www.ebay.com/itm/Space-Rangers-PC-2005-SEALED/183769593691 Kind of surprised at how difficult these are to source. I purchased a retail version several years back published by Excalibur Publishing (which contains Space Rangers 1 & 2), but I had quite a bit of difficulty getting Space Rangers 2 to work with the HD mod (I wasn't aware that Space Rangers 1 had a HD mod at the time). In the end I used another online version that I had purchased from stardock that worked with the mod.
Fast forward to several months ago and just out of curiosity I tried newer versions of the HD mod (for space rangers 1 & 2) and it turns out that my retail copy of SR1 & 2 from Excalibur publishing can now work with the newer versions of the HD mods. Apparently the HD mod tool detects the Excalibur version of SR1 & 2 as a GOG version, whereas the previous HD mod versions didn't detect the correct version of this retail copy and hence wouldn't install.
Unfortunately the DVD provided by Excalibur Publishing is simply a burned version (not pressed), so I've recently made a full archival/install-able backup on to Mitsubishi Gold Archival media just in case the original becomes unreadable in the near future.
EDIT: That's weird, the link I applied appears to be Space Rangers 2. If you read the back of the game however it does come with Space Rangers 1.
I looked at a few other ebay links, but they all appear to be Space Rangers 2 (With Space Rangers 1 included as a bonus). Sorry about that, seems Space Rangers 1 by itself is probably pretty rare.