Good question! I tend to like chessgames.com for this, for example, with the Old Indian, if you go to the Opening Explorer and input some moves, you can get the opening designation and it should show players who play the lines fairly often.
In this case of Old Indian, I got this result, good ol' Lawrence Day!
http://www.chessgames.com/perl/chessopening?eco=A55
I use my chessbase database. I search one opening and pay attention to who plays a line, then I do the same search for the other opening.
Larry Christiansen has played both.
The strongest player I've found who plays both is Movsesian, but Mamedov has played both somewhat more frequently.
Thank you for your response. I will need to use this method (even though it becomes complicated when I have to search for a three or more component repertoire) and to check the players you mentioned (especially Movsesian, as he plays KIA which I like as well). In general, I think, it is a good method because with a repertoire of one player (rather than few openings played by few players) I may expect a kind of consistency in style and approach, which can be a good thing for a beginner like me.
Strikovic Aleksa http://www.chessgames.com/player/aleksa_strikovic.html
Often plays the Philidor and a lot of old Indian lines.
Today's top players don't really do repertoires the way they did in the 1970s and 1980s. The top players today can play almost anything. There are some who specialize in a few openings, like Radjabov and the KID or Kamsky and the a6 Slav, but even they will play any opening on a given day.
It's often a good idea to follow the repertoire of a mid-level GM, 2500-2600 rather than the most fashionable lines played by the elites.
Hello. Do you know if there is any search engine / database, where I can look for players who play a particular set of openings? E.g. I'd like to find a player who plays both Philidor and Old Indian Defense on a regular basis.