Only heirlooms, DesertGirl? Does that mean you won't be ordering from the
Chile Pepper Institute at New Mexico State University in Las Cruces?
Okay, okay . . . leave that aside

. I was going to say Seeds of Change in Sante Fe. They send me a nice catalog (of expensive items) each year. But, I see they've pulled quite a few negatives on the GardenWatchDog last year. I communicate a bit with gardeners in the high deserts of Colorado. One orders from Heirloom Acres but I see the same, recent negatives . . . :/ ?
Another 2 dry-country gardeners swear by
Skyfire Garden Seeds.
Now, I'm in a fairly dry country too and grow several heirlooms. I just learned that the Utah Sweet Onions that I grow are considered heirlooms by some

. My heirloom seed comes from
all sorts of places (including my grandmother who passed away 20 some years ago). I don't order from a company that sells heirlooms, exclusively.
For tomatoes and peppers,
Tomato Growers Supply just seems to me to be a very fine company. And, I'll order from Casey's Heirloom Tomatoes in Calgary for the 1st time soon.
Steve