I think it's random? He's been feeding birds, playing the tambourine, and drinking coffee and stuff pretty regularly. I play exclusively between noon and 6.
You need to choose the Heya, Harv! dialogue option only when he's feeding birds. No other time works.
Just let him do his thing and when you catch him feeding the birds you'll get them. This morning I caught him and I spoke to him at least three times until he finally gave me some.
Update, I saw him feeding birds today, so I spoke to him and he gave me throwing beans again! You can do it unlimited times! I didn't have any beans in my inventory, though, so that might make him not give you more?