Where can I get replacement picture tubes for my Signature 2000 television set?

I would not think that they would exist now, Tubed televisions and monitors are very old technology and when I was working in the mid 90's there was almost none spare around.
What existed was put straight into the production line.
I have another concern that some of the last tubed monitors came with what I call an extra focus to compete with flat screens sharpness. This resulted in a flyback transformer that had three presets on it, those I came across had blown up their respective tubes because of over voltage applied.
It would be worth checking if yours has this development and if so then I would give up because parts will not be around.
If you have a blurry/soft picture due to low emission then a heater booster transformer to give it an extra 10 or 20% but they may not even exist now, if it is going bright or dark then that may be a sign of G2 voltage problems which is that transformer issue and destined to "pop"
You may be lucky but I would not bother, sadly a sign of the times as they say.........

Note the manufactures' name, and buy one made by them.