You can get one from SPA if you're patient. It seems the production run for the Matt400 special is gone. The last person I talked to about it had to wait for it to be hand-delivered from overseas.
Also DLeno is working on one. I've heard it's a DiPricol gauge, so hopefully it will match the interior.
SP Diesel is working on a new pressure box and monitor that is supposed to be available by the end of the month.
TS Performance has a new monitor which will display 4 values at once, plus an optional heads-up display that will display any reading including fuel rail pressure.
Finally, Quadzilla is almost ready with their new monitor, which sounds really awesome. It will display something like six parameters, and have the ability to control almost any performance module on the market---Edge Juice/Attitude, Edge EZ, TST, Xzillaraiders, Ramifiers, MP-8's, you name it. I personally can't wait to see this one.
I'm waiting for a gauge, however. I would like a monitor, but already have a TST w/R49 and a full set of gauges. The only other items I want to monitor are fuel rail pressure and oil pressure. I'll probably go with the DLeno gauge or the SPA.