For the people that think it has been patched, it hasn't.

Can be done right after the chapter 3 mission "Horse Flesh For Dinner"
This mission will unloch the horsefence wich is needed to complete the Bandit challenges.
After all challenges are done, except the Herbalist ones, finish Gambler 10 while replaying the chapter 2 mission "Who Is Not Without Sin".
You can do the Herbalist challenges if you like but they are not needed for this method to work.

In the reverend mission, go all in the first round and call or check when you can in the second and third round.
When there are 5 cards on the table, go all in.
7/10 the NPC's will fold, i got lucky this time in round 3.
If you go all in the second round, there is a big chance you bust out an NPC, this will start the cutscene and no chance of 3 wins in a row.
Abandon the mission, and try again.

After winning 3 rounds in a row, cutscne starts and you will be outside to seek the reverend, the game prompt that you completed Gambler 10.
Finish the mission normaly.

After that you will be back at the point you started the replay and if all things done right, the suit is yours.

Check my channel for more RDR2 videos on how to get stuff early.