Grainger has ASME rated tanks. I bought one for work a few years ago when a crack came in the weld area of a compressor mount. I think a vertical tank/compressor unit is better due to having seen this occur on several horizontal units, I guess due to tank wall flex during pumping. $850 to have the tank welded and state certified for safe use in an industrial setting. The purchased tank was quite a bit cheaper. The plugs were removed from the original horizontal tanks, and the tanks were kept in place to provide motor/compressor mounts. The new tank was piped in downstream. This met state inspection criteria.
RJ