SAI graphics can be only created using the Paint Tool SAI and it's later version, so if you hope for psd to sai conversion, i.e. conversion of Photoshop graphics to SAI, you will need to use the original program. As far as we know, there is really no alternative.
Convert Adobe Photoshop graphics file to Paint Tool SAI drawing.
We found one software available in the database for this conversion.
Microsoft Windows software - convert psd to sai on Windows
A painting software
Convert from psd file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.