I would call up Strawberry cycles in Portland and ask them if they could recomend anyone in the area who might take on this kind of job. They sell frame building tools and may know some local types for whom this would be an appealing project. Portland has a lot of framebuilders, so it's the ideal place to be asking.
This kind of job may be a hard sell to framebuilders. If you can find a guy doing recumbents there is at least the hope of getting over the prejudice factor (I like both kinds of bike myself, but a lot of frame builders who are in business are working on a particular niche). It's also not a standard part and a framebuilder may not stock that kind of tubing. Many do keep some straight 4130 around for custom parts, but there are lots of sizes and wall thicknesses so it may be difficult to get. If the FB has to order in, it immediately becomes a job that probably can't pay. The same goes with the fixturing which they won't have for that part. A lot of frambuilders like have to perfect stuff for the work they do, they don't just jiffy rig a jig, they use specialty jigs. They also may not be equipt to cope that tubing for the joint. The are tubes about that size on most bikes, but they butt with the seatpost, not a crosspiece, and it not the right size for most copes on bikes.
It's a simple enough job, so you might contact metal fabricators like amateur aircraft builders try an EAA chapter, or you might try motorsport or general fabricators since some of them use 4130 extensively.