Well, the thermometer is no problem ... except by searching for it by that name. Here
is one site that has what you are looking for - a lab/scientific web bulb thermometer. You don't need to get the really expensive ASTM certified thermometers - a lower accuracy of +/- 1-2º is plenty close for cooking purposes. I do not know what would make any instant-read digital or dial type probe type thermometer unsuitable for your application.
As for your rub idea - I don't know what about it would make your salmon unsafe for canning because of pH/acidity. Remember, the reason you are pressure canning your fish is because it is low in acid to begin with. Don't know why your idea wouldn't work - don't know about the results. You could even take it one step further and smoke it befor canning if you wanted.
You really might want to read the information on canning salmon at the site Uncle Bob gave you - under the canning section. You might want to also pay attention to the pressure and processing times based on the type of canner you have (dial or weighted) guage. They are not the same.