Where to buy Tri-Tip?

Costco has one already marinated.
Cook high and fast to 135

Alexander's or Trader Joe's.
I grill it on my Traeger.
It has that webbing like brisket. But it's closest to sirloin I'd say. Going to do one this weekend.

Santa Maria style. Sear then indirect until done to your liking. Slice against the grain. It is very popular here in California.

I cooked one a few days ago that was very good. I cut the fat cap off and trimmed all the silver skin off. I salted it down real good and let it sit on the counter for about an hour. Then right before I smoked it I took some paper towels and dried it real good. Basically just sprinkled it with black pepper and granulated garlic and threw it on the grill and cooked over indirect heat with pecan smoke (oddly enough red oak or post oak works best) until it reached 120 degrees. Something came up with the kids so I took it off the grill and let it rest for about 15 minutes while I dealt with the young ones issues that needed tending to. I got my grill heated back up to about 400 degrees and seared the hell out of both sides for about 5 minutes. I checked the temp and it was around 140 degrees. I was fearful I had overcooked it and let it rest for 15 minutes while I was finishing up the side dishes. I took a real sharp knife and cut against the grain into 1/4" slices. The tri tip was a medium rare and bleed like a stuck pig when I cut it up. I've noticed that about tri tips that juices run everywhere when you slice into them even after a long rest period. I had four friends over that had never eaten tri tip and they absolutely loved it. So basically I reverse seared it I suppose. I think the trick to those things is don't undercook or overcook them. Undercooked tri tip seems chewy. Overcooked tri tip is tough. Seems like mid rare to medium, 135 degrees, seems to be the most tender. I think resting them for 15 minutes or a little longer is critical and cutting against the grain makes them more tender. They are real easy to cook.

I've also left the fat cap on and smoked them like a brisket until they started to fall apart and thought it tasted better than brisket.

I buy mine from a specialty meat butcher shop and the butcher at my Rouses has cut them for me. 10 years ago not many people along the gulf coast even knew what they were. Now butchers know exactly what they are so it shouldn't be hard to find one. If it's not out just ask them if they have one and often they do.