If any program can produce .msk mask files it would be Corel PaintShop Pro from which this file type originates. As the program supports most of the common picture formats, including PNG, it should be easy enough provided the conversion is actually useful or even possible.
Convert Portable Network Graphic to Corel PaintShop Photo Pro mask image file.
We found one software available in the database for this conversion.
Microsoft Windows software - convert png to msk on Windows
A professional photo editor and manager for Windows
Convert from png 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.