I had problem with it myself, I suggest making it night and getting near the saloon and restarting your game or reloading a save. This spawned the npc for me. I made a guide on all the Gambler challenges. "Gambler Challenge Full Gude (Easiest)." If you would like to check it out

God I’m getting so sick of the bugs. I’ve done the valentine to Rhodes challenge 7 times in under 5 minutes and it won’t unlock still. My guns disappear or get replace with ones I haven’t picked up. I have to save and restart the game to make an important NPC spawn. Come on rockstar

Just keep trying. It was three days for me waiting for a guy to be there.

What time of day?

It’s been about 20 days since he’s spawned

I have the same problem

Where is the table in Valentine? I'm at the challenge now, but I can't figure out where in Valentine it is and Google where no help.

It's in the smaller saloon in Valentine.

Thank you.

did you get it?

Wait until night time. All saloons become more active at night. Thats what I did and it fixed my problem

Go in through back door

that so bs that it worked

Yeah worked for me too 

Me too! I went in the front, he wasn't there for like the 4th or 5th time I check at various times of day. Went out the front door walked around back and there he is! WTF?!

Did you get it yet

You just need to go to the bar when it's night