Choosing "widespread" parts
You can use online parametric search engines and then sort by in-stock quantities to get some clue as to the most popular parts in the industry. Especially good if there are multiple sources for the same part and/or other suitable parts that are pin-compatible.

A more subtle thing is the intended applications for the parts. If they're mainly used in a fickle market such as cell phones or a dead market like CRT displays ( think horizontal output transistor in your case) they may not be available next year, or they may be bought up by speculators in the gray market and resold at many times the original price.