The ZERO aftermarket replacements on ebay/amazon, are garbage - I bought one and returned it due to the lens shape not totally being correct, and the lens curvature isn't the same but flatter making fitment a struggle. In the off chance you get the lens fitted they have this trippy quirk where you'll see your own eyes' reflection on the inner lens, it's like ghosting effect of sorts.
Finding a OEM fire replacement will likely be tough, for w/e reason these weren't as popular as the Crowbar model an I think discontinued for last ~7 years. I know Buckmans still has some lenses left over for this model when I checked last fall, otherwise maybe you'll find something on Amazon or AmazonWarehouse.
Thanks for the information @Steve Thompson and @BoostBear . I will try to the places you mentioned for the lenses. If not no big deal these are usable.