This is a basic walk through TAB in Finale. Unfortunately, it does not address your issue. If the symbols you want are there, it doesn't say. Although I've been a player for over 50 years, I haven't looked at TAB since the Pete Seeger book when I was in high school so I don't know if the standard guitar symbols will apply.
You can always add them manually using the Graphics Tool. If those characters are found in the Maestro font, that makes it easier.
Since this is a banjo question, you might want to see if other players may have some tips for you by asking this over at the Banjo Hangout. You will also get a lot of unsolicited advice about freeware but that can't be helped.