Marathon Fusion has claimed to discover a scalable way to produce gold via fusion: https://www.inc.com/chloe-aiello/how-this-energy-startup-stumbled-on-a-new-way-to-produce-gold/91218905

By January 1, 2029, will there be synthetically-produced gold that I can buy, as a random U.S. citizen?

The definition of synthetic gold is a substance made of atoms that have 79 protons due to the intentional actions of humans. It doesn't matter whether the gold was produced with fusion or some other method. I should be able to buy at least 1 gram of synthetic gold for $10,000 or less (current prices for regular gold are about $110 per gram). The synthetic gold can be mixed with other metals. I don't plan to actually buy this gold, but it should be possible in theory.