If you have the large Master Cylinder, the matching large booster is available from O'Reilly Auto Parts.  Here is a link to the unit:

 Search for 518000 | O'Reilly Auto Parts (oreillyauto.com)

 It is part number: 518000.  It has the needed residual pressure valve.

Do not use this booster with the small master cylinder. 

If you want to convert from the small system to the large system, you will need Napa M2134 Master Cylinder.  You will also need to adjust the length of the push rod that activates the master cylinder.