WhiterValkyri's solution is correct except it doent take extra collectables as you start with some which are not included in the count for the achievement. These are given at the start as they were only available on the dreamcast version by using the shenmue passport which was later closed down. This feature was not relaunched for this version so they instead put them straight in to your collection.
So you need to get 50 in total collected yourself from either the 6 toy machines.
5 are obtainable from the forklift races 1 for coming in each position.
In the stores if you buy either potato chips or chocolate your can win these from the store raffle, each store has a different raffle which can be viewed in each shop usually on the counter or advertised in the window. I will update with a list once I get a chance.
You can win them for completing the arcade games hang on and out run with only 1 credit.
I believe there are a few more which I will update when I get to them all again.
If there is any questions please let me know and I will try to direct you to specific ones if you are wanting them all.