plain old garden lime and gypsum. i mix that stuff 1:1 and distribute it once or twice a year on the surface with a hand trowel. you could also be extra fancy and crush beautiful crystalled quartz to a powder, compost it in a bull horn underground through march and april, retrieve in may and apply minimally by foliar with about a gram per 13 liters of water per acre. good chee from that method and goes well with composted clay.
this ones labor intensive but if you have a cement mixer,,,, then mixe in clay soil with your garden bed soil. 1:3 clay to soil and mix it mechanically. then dump it back into the bed. it lasts a long time when you mix clay into hummus rich soil. i try and add it to potting mixes and then recycle those into my raised beds. but im only 30x30 at the moment so that's a workable option for one guy.