Sorry electrikmagik, I automatically thought about Marten speakers from Europe.
Their bottom of the line is $6500.00 and climb to $50K and beyond. Guess I must have been asleep, you typed Martin but I read Marten.
From your response about the sound of your system, it appears your completely satisfied with it's performance with compact disc. I would stay where you are unless you have a burning desire to go into another format or seeking older recordings that are plentiful on LP.
As for sound, I think LP is much better. Problem is it costs a fair amount of money to acquire an additional format, more so for LP than CD.
For instance, if a person had an LP playback system and just wanted "background" CD, you could buy a new player at Best Buy for less than $100.00. That's pretty much impossible with LP, not many choices for turntable, arm and cartridge for $100.00 (assuming your Sansui has phono built in).
Are there that many brands and why aren't they in stores?
There are lots of brands. But again, the LP format is old technology and most of the kids are moving toward MP3, which is worse than CD or LP (in my opinion). There are tens of dozens of turntables available both new and old, and many new ones still being designed and built today. Unless you venture into a specialty high end audio store you're unlikely to see any turntables out on display.
If you're determined to add a turntable to your system, I and others here at Audiogon will help you find your way.