i have one of those replacement "heat stove tubes" from a 70's something [universal perhaps ?]
i just bend it to whatever shape i need, then go to the local parts store [o'reily's and napa] and match it up to something on the wall.
most of the time the hose needs trimmed on both ends.
i also bend some 1/16" wire around a broom handle, then insert it into the lower hose to prevent it from collapsing if it wants to do that.