I know this is an old post, but for any one searching I thought I would add what I am doing. I have the grace frame and it has the wooden tracks. I did go to a machine shop that cut the 1/4 inch steel rods for me. There are two kinds of steel heat rolled and cold rolled. I purchased the cold rolled steel and it is a lot more expensive than what others have posted they purchased theirs for. It ended up costing me $30 for 2 rods for the track and 2 for the carriage.
They fit my carriage fine. But my wooden track the 1/4 in rods slide to deep down. I will purchase some type of cord, nylon rope or something to set below the rod. That way my carriage wheels will not hit the wooden track.