That’s not an easy question to answer.
A distiguishing feature of Palma is a level playing field. No competitor is supposed to have an advantage due to equipment. Rifles have to meet very strict standards. In general, the only cartridge that is used today is the 7.62MM NATO or it’s commercial equivilent, the 308W. ( In the USA, some matches can be fired with the 5.56x45.) Rules call for an unmodified 7.62mm case and a maximum bullet weight of 155 grains. International Palma tries to maintain that level playing field by having all competitors use the same ammunition. It is actually issued on the line similar to the way the old National Matches were conducted. Competitors pay for the ammunition either directly or through entry fees. The host country is responsible for supplying the ammunition. To keep things fairer still, some even issued the rifles to be used. After the matches the competitors could buy the rifle and there were always collectors and other shooters waiting to buy any that the competitors did not want. (Host supplied rifles was stopped in 1983)
From time to time, a commercial company will manufacture a special lot of Palma to commemorate an event such as the USA 1976 Bicentennial. They do this partially as a promotional and public relations thing. The WW 1976 ammunition was made in one lot of 25,000 rounds. I believe they gave boxes away to competitors, as souvenirs, and anyone could buy it if they so chose. You can still find boxes of it for sale on the various auctions. I believe Australia had the 1988 ammunition maufactured to their specs especially for the matches which was the first ever held in OZ. In 1979, New Zealand hosted the Matches but there was no commercial manufacturer in NZ so volunteers handloaded all the ammunition required, using Australian components.
Lapua just recently started manufacturing their own Palma ammunition with a small rifle primer. It may catch on, or it may not. There will always be a commercial manufacturer ready to jump in and cater to the matches.
That’s the way it was. I can’t say how things are done in the 21st Century but I would guess it’s similar if not the same. But, some young Palma shooter will probably chime in and tell us that things are different now and old men should stay in their Century.