Found these new Cornelius brand secondary regulators for 15 dollars each on Fleabag. Keep in mind they are right hand thread so if you are adding to an existing lefty you will need the adapter Midwest sells for under a buck.
https://www.ebay.com/itm/C02-Gas-Pressure-Regulator/254187461755?hash=item3b2ec0dc7b:g:JRAAAOSwwnVc
5F~m
https://www.ebay.com/itm/C02-Gas-Pressure-Regulator/254187461755?hash=item3b2ec0dc7b:g:JRAAAOSwwnVc