They only film 8 episodes a season. They've shown at least 6 new ones on showcase this year (and probably all 8, but I was away for a couple of weeks). Check out their web site for descriptions of all the episodes. One of my favorite shows!
Yeah, most Canadian shows don't produce more than 8-10 episodes a season (unless they get foreign backers like Lexx or Due South). All 8 episodes of Trailer Park Boys have aired this spring (mostly April and May)and there will be a fifth season, as well as a low-budget feature film (budgeted at $5 million, which is still light years ahead of the original B/W film/pilot).