I recently replaced the wheel bearings and seals on my 2018 Speedmaster and I found the OEM ones were NSK brand and I could get these for 1/3rd the price from Simply Bearings (https://simplybearings.co.uk). I made two purchases and the free delivery option came next day by 1st class post. 
The same wheel bearings parts are used across most of the range of modern Triumphs so I thought it would be useful to show the OEM part number and link to the exact item I bought. Assuming OEM bearings are standard tolerance sort, not some special ones, then the bearings should be identical items. The seals are of a random brand but same twin-lip construction.
| Triumph Part | Alternative |
|---|---|
| Front wheel | |
| T3800702 | Bearing NSK-6004DDU |
| T3600703 | Seal 30x42x7mm (1mm deeper than OEM but lots of space on my wheel) |
| Rear wheel | |
| T3800703 | Bearing NSK-6204DDU |
| T3600701 | Seal 28x47x7mm |
| Sprocket carrier | |
| T3800029 | Bearing NSK-6205DDU |
| T3600073 | Seal 35x52x6mm |
