Check out The Man in Seat 61 website - the authoritative source for this kind of info.
This page gives info on Moscow/Riga journeys and a recommendation for buying tickets (scroll down if the link takes you to the top of the web page).
You can buy a ticket directly from RZD for the direct train at 17:06 from Moscow. It may be too early for your date.
http://eng.rzd.ru
E-tickets are available.
You can buy a ticket directly from RZD for the direct train at 17:06 from Moscow. It may be too early for your date.
http://eng.rzd.ru
E-tickets are available.
When are you planning to do this ? I'll be in Riga from June 3rd - 7th