How many are you expecting per year? According to this web page, it looks like an average of 3-4 a year.
http://tripleplays.sabr.org/tp_year.htm
Here's an analysis of triple-plays per 1000 innings based on decades. Depending on the era, you could have had quite a bit.
http://tripleplays.sabr.org/tp_analysis_ham1.pdf