My oncidium/Odontoglossum are in a mix of orchid moss and better gro special mix, it dries well and drains well too. Good luck and good growing, remember these are one of those types of plants are pretty sturdy, trust me I almost fried mine in the Texas sun and now have 2 new growths...Though I would not try that myself. BAHAHA. Also as stated above by another member seaweed extract won't hurt either.
In my hick town I have to special order everything. Some of the larger towns depending on where you live, variations of it is available in places like Home Depot, lowes... etc..., I ordered mine on ebay and got free shipping. mine is Gro-more (?) I think, I always forget. It is thick and black but not to strong a really strong fishy order that I have smelled thus far.
Haha im in a little town ! But I have some fertilizer sticks and stuff yoy mix in water from home depot. But I will have to look into the seaweed haha!
I use bettergro, too, then add extra calcium, Epsom salts and the Ironite slowly dissoving on the bottom of the watering can. I have the MSU fertilizer and use it now and then.
I was thinking of ordering the MSU as it appears to be "the best" but so far, I'm seeing growth with the better gro orchid plus fert. I've got new roots growing and a new leaf showing up on a phal that I rescued that I thought was going to die and I haven't even cut the spike on that guy yet. I wanted to enjoy the flowers for a bit longer before I cut it down.