Ball bearings and thumb studs.

[Ten4leader]

I've looked for a bit now and I haven't quite found a knife that has a thumb stud and bearings, only flippers. Is their a reason why?

 

[Hiro-kun]

Probably because bearings make the flipping action much smoother and effortless.
The original Boker Kwaiken has bearings but no flipper (opens with a thumb disk). A lot of fans clamoured for a flipper version and got one.

 

[chrisk91]

Thumb studs aren't as picky about smoothness as flippers.

 

[Jay S.]

How about the TSF Beast? Full custom with ikbs and thumbstuds for around $300.

 

[bigmark408]

Bearings are not needed....try a fluted military or a Scott Cook....just a quick couple distant examples.