Mesa has two types left. One for the MK IV with no tabs and one for the MK I-III with the two tabs that grip the chassis behinde the faceplate.
If you have a Simul, you will have to take the faceplate off and unscrew the power board to get to the EQ. The you have to bend all of the upper and lower tabs to release it. It is a major pain in the arse. I dont think they have IIB slider knobs anymore.