Q.can I grow an okame cherry in a pot?
I cannot find suitable space for my okame and wonder if there are ways to keep it small?

Yes, the okame cherry can be kept smaller in a pot or planter. You can even make it into a bonsai. Some strategic pruning is all it takes!
Here are some great articles on how to grow trees in containers:
https://www.gardeningknowhow.com/special/containers/how-to-grow-container-trees.htm
https://www.gardeningknowhow.com/ornamental/trees/tgen/growing-trees-in-containers.htm
https://www.gardeningknowhow.com/houseplants/bonsai/bonsai-basics-starting-your-own-bonsai.htm