I went the opposite way, replaced an '06 round with a later bullet headlight off of a highball. Some highball folks prefer the round light, some Vegas owners prefer the bullet. The wires stuff into the innerspace of either. I did have better luck reducing nod after going round->bullet by changing the mounting post as well. The reflectors are probably different between the HID and Halogen bulb options, but I think most bikes are halogen. I'm not aware of significant differences to worry about between Halogen series.
So ebay, disassembler (pinwall, etc) or post to other subforums for the models that came with what you want.
2006 Vingpin, Inverted forks, Progressive rear shock, Stage 1 slip-on kit, S+S intake, grips and pegs, tach and rack, corbin saddle, night dragons. KMC reflashed/retuned to 100HP/104 TQ, good'nuff.
2014 BMW 650i Xdrive
2005 Grand Cherokee Ltd 5.7L Hemi, Konis, SRT swaybars, BB
1986 Porsche 928S, slightly enhanced.