If you want to stick with the factory grips, but don't want to pay outrageous prices, then order two of BMW part # 32 7 22 332 619. This is listed as Left Grip, Unheated, but the rubber grip is the same. What you do is carefully cut the old grips off, then remove the new rubber grip from its plastic tube (which you don't need), then slide the new grip over your existing heater elements.
Or if your existing grips are worn but not damaged, go with the Grip Puppies. They'll cover up the worn grips, and also give you a slightly thicker, padded grip. With my large hands, I add Grip Puppies to every new bike just because they're more comfortable.
As far as wind guards, you have two options.
The AeroGards work really well, and keep the wind off of your hands and most of your arms as well.
Or if you're mostly concerned with just the hands, you could go with the factory hand guards from an R1150GS. These will screw right in to the end of the GT's handlebars using the factory GS hardware. You'll have to make up some small brackets to hold the inner end of the guards, but that's not too difficult.
You want parts # 2, 3, 4 from the diagram below.
#2....32 71 2 328 693....$26.88....1 pieceÖ..Hand Guard, Black, Left
#2....46 63 2 328 694....$26.88....1 piece......Hand Guard, Black, Right
#3....32 71 2 328 841......$7.02....2 pieces....Clamping Bush
#4....32 71 7 660 005......$2.37....2 pieces....Countersunk Head Screw - M8X40
So for $72.54 plus a bit of work, you have an option that looks factory.
Or you can order from Countryside BMW and use the PROMO15 code to save 15%, although in such a small order it'd probably be a wash with shipping versus local sales tax.
'13 Dark Graphite Metallic K16GTLD, 24K miles and counting...
'09 Magnesium Beige Metallic K13GT, 60K miles miles and counting...
'02 Mauve Metallic K12LTC, 106K miles and sold
BMWLT#145, IBA# 366, MOA# 111996, SCMA# 24032
All lower 48 states plus Alaska on the K13GT in two weeks . . .
Some people see the gas tank as half empty. Some see it as half full. All I care is that I know where the next tankful is coming from...