I have never seen one for sale at any online retailer. Every once in a while they pop up on the secondary market. There was one on bayoushooter a month or so ago IIRC
They are LE specific guns to be used for training. I was able to order one through my LE distributor, but had to provide my armorer certificate and get my sheriff to sign a letter for me that I would use it for LE purposes.
If you keep an eye on gunbroker they do show up on occasion.
They're not released to the public, just law enforcement. It’s a collector for most due to the rarity. Also, they’re not listed on Glocks website anymore.
You can get a self reset trigger and drop it into a regular glock. I considered it when I wanted to use a laser trainer but buying the SIRT pistol was cheaper.