Absolutely agree. I learned to play on clock in a different game system, but it was really helpful in teaching myself how to cut through analysis paralysis loops.
If any of your local stores have a large Warmachine or Guildball community you may get lucky as they may stock chess clocks, due to both of those games needing them to play.
Also, if you have an old phone you upgraded from (iphone 2 or whatever) look for a chess clock app that will still work on that version of the OS. Or even just use it as a timer like RobertShepherd suggests above.