Even though we call them tensioners (they do that) because the tension becomes fixed they are basically idlers. And in that regard it is an adaptable part with a little fabrication. So, if the part ever becomes unobtanium I'm sure it came be replicated.
Timing belt side note: My son inherited his grandmother's 1996 Mazda Protege. The good news it only had 40,000 miles. The bad news, the timing belt was 23 years old. Surprisingly the belt was still supple and was void of any cracks. Prudence still required we replace it. Even though the new Gates belt we received from Rock Auto came in a box the packaging seemed rather old. I inquired of Gates and they said the code indicated it was 12 years old. We returned it and they shipped us another..., without a box. In the end we decided that an unused 12 year old belt was better than a 23 year old belt with 40,000 miles.
I mention this because I wonder as the years go by if the timing belts available for older engines will only be NOS (New Old Stock) and as aged rubber parts, questionable.