Regarding Dan's suggestion of fiberglass; an old trick from my days of making model aircraft is to get some plastic sheeting, cut it into long strips. Then put a thin coat of resin on the foam. (The resin may melt the foam especially if you put too much resin on. If it does maybe coat it first with a painted on thinned wood glue.) Then wrap the fiberglass tape around the foam tightly. It may work better if you do one section at a time say one half at a time. Then put some more resin on the cloth. Do not put excess resin on, as the resin is only there to smooth out the cloth and hold the cloth in place. Excess resin just makes it heavier. The strength comes from the cloth. Then you take the long strip of polyethylene plastic and wrap it very tightly over top of the fiberglass cloth. This will make it smooth as... glass... oops. Hold this in place with masking tape or whatever. After the glass hardens remove the plastic.
Then to join the ring to the pole get a union as descibed below, and fit it to the ring, either by cutting out part of the ring before you glass it or cutting off part of the union so that you just push it in place and then glass over the join and then finish fiberglassing the second half of the ring.
Then sand off the coating that surfaces from the edge of the cloth after it dries so that it will bond to the coatings for the other half which you do in the same way.
The trick here is that the polyethylene makes the fiberglass smoooth.
If you decide to go for the metal pipe, (I wouldn't) go to any electrician's shop where they have pipe benders of different sizes for bending electrical conduit, or go to a building supply place and get some plastic plumbing "thingies" (or metal) that are used as elbows. They come in different sizes and angles. You just join them together with a union joint (not sure of the name) that would attach to the pole. Also you could use the elbows used in household central vacuum systems that also come in various sizes. Also they have union pieces which would make it possible to join it to the pole. Only problem here is that folks might be tempted to infer that they... "suck".
One other possibility is to go to a Kiddies store.... (Toys Are Us. frinstance) and look around. Probably something there that would do for a ring.
I am speculating that this would work as I have not tried it. My Tiger has a snuffer installed.