If you just need to “get it done” somehow, then use the ready made Swing expression in the default expression library.

If you - On The Other Hand - need to have full control over all the items in the symbol (such as notehead size, stem thickness, triplet number positioning, &c.), then consider using the Shape Designer to create a new, custom shape that looks exactly as needed.

You can use your new, custom shape as a shape expression.

Or you can create this expression using the MaestroTimes font. All of the characters you need exist in this font. Check the help documentation to see what keystrokes will give you what you need.

Here is the swing expression without the word "Swing" in Maestro Times :

In an expression, paste this 

ŒÂ = Œ lj

Select this text and change it to Maestro Times (in the size you want).