What are the statistics for the last 50-100 years as to how many people convert and become Geirim yearly?
In the US, about 1.5% of self-identified Orthodox Jewish adults say they had a formal conversion, according to data from Pew's 2013 survey of American Jews. This amounts to about ~7000 people. (According to this article, the RCA says that 1275 people had converted with an RCA-affiliated beit din over a seven-year period, although, as the article says, plenty of Orthodox conversions take place outside the RCA's system.)
Research by the Israel Democracy Institute says that 80,000 people converted with the Rabbinate from 1995 to 2015, including 45,000 from the Ethiopian community who underwent giyur l'chumra.