I obtained the parts here: https://www.motorcyclespareparts.eu/piaggio-parts/scooters/beverly-350-4t-4v-ie-e3-sport-touring-2014/rear-headlamps-turn-signal-lamps-643130.aspx
But the parts are also available from a site sponsor (Motovista)
This is a straight forward mod. You have to remove the rear tail light assemblies. I used this source to guide the disassembly: http://www.wotmeworry.org.uk/manuals/Beverley/BV350/BV350%20Workshop%20Manual.pdf
Page CHAS - 323
The 3 wire light plug that goes to the tail light also carries a wire for the brake light. The US version does not have a functioning brake light wire (Yellow with black stripe). See pic below. You will end up splicing the tubing to expose about 3" and splice the US active brake light line into this line.
Black = ground
Orange/yellow stripe = running LED lights
Yellow/black stripe = brake LED light
The current US brake line is a 2 line strand. If you roll back the rubber covering, you will see the Yellow wire with black stripe - see pic below. You will slice down this tubing and cut the Yellow wire with black stripe. You will solder a 5" length of wiring to the hot line and solder the other end onto the 3 prong wire loom. Repeat for the other side.
The next step is to disassemble the turn signal wiring from the turn signal stalks and route them back up the back of the bike. These wires will be connected to the bulb holders in the European tail light assemblies.
Once done, you will have clear lens with LED tail and brake lights from the center and amber turn signals on the outside.
If you are tight on budget, you can use the US tail light assemblies. Your end result will be red LED tail and brake lights and your outside turn signals will signal through the outside portion in red.