As Jacob says, 1/4 rod cut to length say 1". I was doing that 45 years ago as a cheap/only solution and they were still OK 40+ years later. Take the same care to set out positions/spacings and 'Bobs your uncle'. Fancy things weren't around then or not easily obtained. MS,brass,SS, even plastic rod. Same with bookshelf ends....rod bent into a 'U' shape and shelf drill close to the end. IKEA do in nowadays! Good luck.
These people are handy for shelf supports - in 5, 6 or 7mm sizes. If you want to fit into 1/4" holes, they also sell metal sockets which have an OD of 6.3mm which is very close to 1/4" so could work as a converter. Or just drill out to 7mm.