I went through this about 2 years ago. Our Holston gas company in town said they recertified them but they had to be sent off somewhere for several weeks or some **** and I'd imagine it would cost ME to ship it off with them. So I checked around to all the local gas companies and most of them didn't recertify tanks, finally found one in Fort Payne that did and in 2 days I had recertified tanks. Seems like it was over $100 for 2 tanks, because they replace the valves and that counts paying for parts and labor. I bought another 10 gallon tank while I was there and had both 10 gallon tanks and the 20 lb tank filled too, so my bill was like $350, so I don't remember exact recertification costs.
You just have to call around to all the places in your area til you find someone that will do it.