I have not seen a complete list but have assembled some data that should help you. Please verify your engine bearings and seals match these numbers or sizes before you buy them. Bearings were changed between some years. Many of these bearings are industrial bearings that you can get off ebay or from a bearing shop.
GasGas Transmission bearings
Bearing #
Counter shaft bearing 6305C3 Grainger #4ZXJ1
Countershaft Seal 30x40x7
Clutch bearing 6205Zc3E
Trans shafts 6203c3 Grainger #4zxe8
98-02 Crank 63/28c3 or 63/28 maybe All Balls Part Number: 24-1112
Ignition crank roller Bearing, NJ206ET-C3 or KTM ? 50330082000 which has higher c3/4 tolerance
Note that some engines (250 and 300) went to roller bearing on the ignition side. The 2001 Xc250 had the roller bearing but the 2004 200 had two ball bearings. which are the same bearing as the Honda CR250 1990-2008, Honda CR500 1989-2002, Kawasaki KX250 1993-2008, Kawasaki KX500 1993-3005, Suzuki RM250 1999-2007, Yamaha YZ250 1989-2013
Someone tried this in a 07 300 -NJ206 ET -C3 (LHS) and 63/28-c3 (RHS)
Not sure if the crank seals the same as the 01 02 models ? ie kok 20x35x6 -viton (LHS) and kok 38x52x7 -viton (RHS)
1 x SMALL END BEARING INA KBK 18x22x22
1 x LHS CRANK BEARING SKF NJ206ECP - C3 (this should be the ET not ECP)
1 x RHS CRANK BEARING SKF 63/28 - C3
1 x COUNTERSHAFT BEARING SKF 6305 - C3
1 x LHS CRANK SEAL KOK 20x35x6 ? VITON ktm 47030076100 (2004-14 105 85 65)
1 x RHS CRANK SEAL KOK 38x52x7 - VITON ktm 0760385273 (1994-14 250 300)
1 x COUNTERSHAFT SEAL 30x40x7 Suzuki 09283-30061
Shift Shaft Seal 12x22x7
KICKSTART shaft SEAL 20X30X7