Users searching for ma to 3ds conversion are typically looking for a way to convert Autodesk Maya content to 3ds Max, typically in case they lack access to Maya for the export.
With Maya you can simply use the File ► Send to 3ds Max ► Send as New Scene option, but without Maya you probably have to rely on some 3rd party solution or on one of the popular exchange format, for example FBX. Still you will need someone to export the .ma files for you.
Updated: October 13, 2023