Based on location, Sequioa-Kings Pack station, a/k/a the Berners, may be the best choice, if they do it. They are based in Independence and supply up Kearsarge, so I suspect they are the closest pack station. However, I believe these pack stations are required to be licensed for commercial activity, and so there may be an issue as to whether Shepherd Pass is within their license. I believe it is quite pricey for Kearsarge -- something like $600-800 if you want them to meet you at the JMT, though cheaper at the pass. I imagine the custom trip to a different pass might be more, although you are looking to meet at a pass, not the JMT, which helps.
Here is a list that someone else created of all the pack stations supplying the Eastern Sierra. The Sequioa/Kings aka the Berners (Brian and Daneca) are listed down toward the bottom. They operate out of Independence.
http://www.owensvalleyhistory.com/pack_stations/page54.htmlI note that Inyo NF says that the trail up to Shepherds pass is frequently impassable to stock.
