Yes there are a lot of Sea Buckthorn orchards just feeding the crows! The best approach (according to the University of Sask.) is to shake and collect the berries on a tarp. they attached a vibrator to the boom of one of those mini rubber tracked excavators it causes a bit of tree damage they say. Because the fruit when ripe has a lot of cling to remove from the stem, I heard they were trying to breed a variety with less cling so shaking would be easier. On my orchard I tried the more affordable attachment that goes on a portable reciprocating saw, it pinches the branch and shakes off the berries. The one I had whiplashed the branch off before all the berries shook loose. I've gone back to pruning to harvest. Once the trees are established they seem to handle the pruning and give the same amount of fruit the following year. To larry-gene I run my fruit through a juicer(auger type) and the seeds and some skins come out the solids section, like a lot of fruit, it clogs the screens though.

Abuse them. My Okie summer last year was awful. All the seaberry got was a splash as the hose went past, between the strawberries and the goumi, which needed water all the time. The seaberry got a decent drink when I watered the lawn every 10 days. It took me a while to realize that I have seaberry fruit this year! They are a very inconspicuous thing.

I don't know of any nurseries selling it but there is a sea buckthorn supplement manufacturer in Chicago. They're called SeabuckWonders. Here is a link that might be useful: Sea Buckthorn Insider - The Authority on Sea Buckthorn

I'm not sure but I think the acidity of our area (neutral or slightly acid water/soil) is different from the environment they are used to. I also think that day length and sun strength plays a role. I know when I try to grow plants from South America that are found high in the Andes Mountains, they don't know what to do with long summer days. Close to the equator the days and nights are pretty constant at 12 hours each. Other failures for me are Goji - which thrives and is highly invasive but rarely fruits. Princepia - which barely grows but blooms, it loves our winter but hates our summer. Quince, Serviceberry, Medlar, and all of the Mountain Ash hybrids (Ivan's Beauty, Ivan's Belle, Shippova) all suffer from Cedar-Quince Rust, Cedar-Apple Rust or Cedar-Hawthorne Rust.