Welcome to chowhound! While Paso is not known for tri tip--that would be Santa Maria, an hour to the south--others more familiar with Paso may have the info you seek.
But I'll repeat my caution that tri tip is best served at once off the grill, never held. Restaurant offerings are going to be poor unless it is a steak (sometimes called a coulotte) cut from a whole tri tip roast and grilled to order over hot oak coals (never flames). I like to do this with a whole roast at home. Trim fat, leaving some here and there, cut cross the grain into 1 1/2 " steaks, then marinate or apply a dry rub and cook fast to rare over med-hot coals.
Tri tip actually takes well to marinade or dry rub. Although it is no longer in the Santa Maria Style BBQ tradtion, it is very good. I like to use teriyaki, jerk or a standard paprika-based garlic salt & spice rub.
J&R meats in Paso and Templeton could supply you with a good roast to take home.
Hope you enjoy your stay--if you get out and about, please post about your experiences!