Welcome Bob!
I'm in southwest Missouri and we won't be seeing many plants for sale here until April. I can't recall if I've seen tall evening primrose for sale locally in the past.
What big city/town are you close to? Maybe someone here can give you names of good garden centers to visit.

I have seed for the tall yellow primrose. If you cannot find plants email me at webmasteratgohsdotorg and we will work something out. Personally I think they are weeds and rank right up there with johnson grass and morning glories.
My wife planted them from seed they bloomed the second year and she has been pulling them out ever since. Be careful on what you ask for!!

Lee

I don't know where, but I can tell you what to ask for:

There are several species of "tall" Oenothera.

Oenothera hookeri

Oenothera biennis is a Eastern NA native and a nice biennial weed.

Oenothera elata hookeri is beautiful but I'm not sure it's hardy for zone 6.

Oenothera fruticosa has dozens of cultivars, all nice and a bit assertive.

Oenothera glazioviana is a favorite.

Good retail garden centers should carry one or more of these. Otherwise, they're available (especially the superior hybrids and cultivars) through several mail-order companies.