It’s a shortage of materials to make the parts that we desire. China is buying all the scrap metal they can get their hands on. This leaves little for the manufacturers in the USA.
You listed the best 2, TTI and Schumacher. Block hugger headers don't work on a-bodies. If budget is an issue, take some time, save some money and get good headers that fit.
Look like 70's/80's Direct Connection dress up valve covers. They're based on stock valve covers but like 66fs said they don't have any brackets or looms to make them universal.