They are currently out of stock at the moment however you can request to be notified and be put on a waiting list. I went through the same issue when getting the Dark Earth Glock Gen4 mag releases and base plates for my G21 and G35.
The G42 magazine release is similar in design to the Gen4 mag releases. They are $16.92 on Red State Tactical’s website. I suspect that these will be as nice as the ones I have on my Gen4 Glocks.
The extended magazine base plates are something I wanted since I first shot the G42 back at ShotShow. But as I don’t have a G42 yet, I can wait for these to get back in stock. They are only $12.75 on the website.