I received my parts manuals so here are the seat part numbers for 2010 through 2013 model year FLHTCUSE bikes. I'll scan the seat pages for each and post when I am able.
The only restricted part listed is the 2011 Tour-Pak Passenger Backrest Kit (I don't know what's so special about that one). None of the other parts are restricted.
FLHTCUSE Seat Part Numbers:
2013 FLHTCUSE8
52000029 Seat, w/ 51652-97A
2013 FLHTCUSE8 Anniversary
52000080 Seat, w/ 51652-97A
2012 FLHTCUSE7
52000028 Seat, w/ 51652-97A
2011 FLHTCUSE6
54112-11 Seat
2010 FLHTCUSE5
52344-10 Seat
Seat Hardware
51652-97A Seat Mounting Bracket
2952A Screw (2)
59768-97 Nut Kit, seat, w/ retention washer
FLHTCUSE Passenger Grab Strap Part Numbers:
2011FLHTCUSE6, 2012 FLHTCUSE7 & 2013 FLHTCUSE8
54113-11 Grab Strap, passenger
2013 FLHTCUSE8 Anniversary
52400058 Grab Strap, passenger
2010 FLHTCUSE5
51577-09 Grab Strap, passenger
Grab Strap Hardware
51690-09 Bracket, grab strap mounting
2952A Screw (2)
6703 Washer
FLHTCUSE Passenger Tour-Pak Backrest Pad/Pillow Part Numbers:
2010 FLHTCUSE5, 2011 FLHTCUSE6, 2012 FLHTCUSE7 & 2013 FLHTCUSE8
53364-10 Backrest Pad, passenger Tour-Pak
2724 Screw (2)
6716 Washer (2)
90844-80 Acorn Nut (2)
FLHTCUSE Tour Pak Backrest Part Numbers:
2013 FLHTCUSE8
52300033 Backrest Kit, passenger, w/ 51715-06, 52192-86A, & 54164-10A
2013 FLHTCUSE8 Anniversary
52300210 Backrest Kit, passenger, w/ 51715-06, 52192-86A, & 54164-10A
2012 FLHTCUSE7
52300031 Backrest Kit, passenger, w/ 51715-06, 52192-86A, & 54164-10
2011 FLHTCUSE6
52300010 Backrest Kit, passenger, w/ 51715-06, 52192-86A, & 54164-10 (**Restricted Sale Part**)
2010 FLHTCUSE5
52186-10 Backrest Kit, passenger, w/ 7716, 52192-86A, 53515-86, 53517-86 & 54164-10
2011-13 Additional Hardware
53517-86 Cushion Plate, plastic
53515-86 Backing Plate
7716 Locknut (11)
FLHTCUSE Rider Backrest Part Numbers:
2013 FLHTCUSE8
52300032 Rider Backrest, w/ 3540 & 10406
2013 FLHTCUSE8 Anniversary
52300211 Rider Backrest, w/ 3540 & 10406
2011 FLHTCUSE6 & 2012 FLHTCUSE7
54129-11 Rider Backrest, w/ 3540 & 10406
2010 FLHTCUSE5
52586-10 Rider Backrest, w/ 3540 & 10406
FLHTCUSE Rider Backrest Hardware
2011 FLHTCUSE6
52589-09 Mounting Hardware Kit, seat, w/ 3546, 3574, 7531, 7716, 52567-93D, 52585-09 & 52590-09
2010 FLHTCUSE5, 2012 FLHTCUSE7 & 2013 FLHTCUSE8
52589-09A Mounting Hardware Kit, seat, w/ 3546, 3574, 7531, 7716, 52567-93D, 52585-09 & 52590-09