Choose a group from a user input

[ScottF]

Hey everyone, hoping for some help on this one, searched but can't find...
From the list below, I need to get all the lines that contain ##x and put them all in a Dropdown or a Listbox for the user to choose from.

----------
Start

##2
folder#1
folder#2
EndOfList

##3
folder#3
folder#4
EndOfList

##4
folder#5
EndOfList
----------

So the listbox will have... This is what user chooses from.
##2
##3
##4 
etc.

If the user chooses ##3 for example, then need to get all of group ##3 to EndOfList in bold above.

I hope I explained this properly. Thanks ahead for any help!
ScottF