Welcome to Orchid Board
Many people have used a seaweed extract to help boost root growth in orchids. Our member Ray sells it in the USA, he has himself reported very good results from it (he always sells things which he's tested for himself and knows to be good). His investigations of it show that how it's prepared and which seaweed is used have a big influence on it's effectiveness.
His website might be the best place to start. I've not tried his products myself as I live in the UK, but others have reported good results. I've had good results from a seaweed I've tried that I can get over here.
FirstRays
Kelpmax is the product your are looking for. He also does/did a product called 'Solo' which is a combined fertiliser and seaweed extract. It's based on the MSU fertiliser and the Kelpmax. I can't see it on his website which might mean he doesn't have it in stock, but you can always ask if you are interested.