Which crimp tool to use with SSH-003GA-P0.2?
When you go to the Digikey page of the SSH-003GA-P0.2, you can scroll down and see the Tool section.
This specifies the YRS-859 as compatible hand tool.

That is super easy. When there is no tool section, you can look for "other customers also bought", or "relevant products" that you often find at the bottom of any online store. There will at lease be some hints in here to brand or off-brand tools.

It also specifies the tools per part in the table available from JST.
http://www.jst-mfg.com/product/pdf/eng/eTOOL-5A.pdf
Which for JST is obvious, but some lesser known brands might not be clear about this.