I haven't been to any gold sellers here lately but i hear that if you try to buy using the Antam's price the answer usually is 'barang kosong', unless you're willing to pay 10% over the Antam's price.
Yes, physical gold, the gold bars, are sometimes difficult to obtain. A month or three ago, the smaller Antam bars of 20g or less were completely unavailable here in East Java.
The premium you pay for Antam bars has been high for a long time. This morning I checked with us, and it was Rp640,000 per gram (24%, for a 10g bar). The gold price at that time was Rp2,675,000/gram, so this bar would have cost Rp33,150,000.
UBS is another well-known brand in Indonesia. In the past, their premium was a quarter to a third of Antam's, but it could be higher now. Unfortunately, it was unavailable today. The premium on the private label gold from a large gold store chain here was Rp175,000/g (10g bar), Rp180,000/g (5g bar), and Rp210,000 (2.5g bar). This 6 to 8% premium is almost a threefold increase in just a few months.
In my experience, if you buy gold bars in a regular store, you have to show ID. You always receive a sales receipt from the store in your name and a store will not buy any gold (bars) back without this receipt. And I believe you also have to file a tax return. Perhaps for this reason, but certainly also because of the high premium on Antam gold bars, there's a fairly vibrant gray market for them. Buying and selling is done through an intermediary. You can get a better price because of a rather large margin on that premium, and some may prefer it for anonymity.