I have spent a great deal of my life in Latvia, in fact on my last trip I made it my point to try as many different beers as I could find, I had to stop at 24, you can only drink so much.
But I gathered a lot of good information for me to start attempting to make some clones.
I am sad to say but there are no good "Baltic Porters" in Latvia
If you want a good "Baltic Porter" you should try a beer from next door, Lithuania, the beer is called "Porteris" brewed by Utenos.
The closest that you'll get to that in Latvia is
Stauts - Cesu Alus
Porteris - Aldaris
Tumsais - Lacplesa Alus (I think they might have changed the ingredients in this beer over last 2 years as it didn't taste anything like it used to)