The Ten Tec Argosy has a add-on noise blanker, the Model 223A. The schematic is available, but replicating it would be difficult. I also doubt you will find one for sale.
The most popular noise blanker to use as a add-on for older radios is the Heathkit SBA-104-1. These work very well and sometimes pop up on E-Bay. But they are fairly rare.
About 10, or more, years ago I added a home brew noise blanker to my Heathkit HR-1680 receiver. I found the suggestion for it in an old article in Ham Radio Magazine (April 1976). The article was about miniaturizing a receiver, but it included a simple Noise Blanker that used a MPF-102 FET and a few diodes. So I took the Noise Blanker design and adapted to my radio. Here is a few links to some information.
This first link is to the schematic of the
HR-1680 Noise Blanker, showing where I inserted it in circuitry. It is inserted in the IF chain just before the crystal filter.
This next link is a image showing the
Perf-Board Layout. This is the layout of the circuit. The terminals with the black "X" are ground connections on the bottom of the board. This fit in nicely in the radio and can be easily removed.
Note that there is no level control or on/off switching. A level control can be included by adding a variable resistor to the gate of the FET. An on/off capability can be effected by putting a SPST switch in the Source lead of the FET. I always intended to add these controls to my HR-1680, but I couldn't find a good way to add them, without drilling some holes.
Overall, the Noise Blanker worked very well. I still have the radio that way.