Hardness of Titanium on the HRc ? ? ? ?

It ist not very much wear resistant.
AFAIK, Titanium hardness ist too low for HRC.
Michael Dahms

For the very common Ti-6Al-4V alloy, expect about 30-36 HRC, depending on microstructure. It is possible to get into the low 40's with work hardened beta alloys like 38-6-4-4. Yet as the knowledgeable Michael Dahms notes, the wear resistance is poor. The edge holding ability is also poor, so I believe that titanium alloys are just wrong for knives. Great corrosion resistance, of course, and it's sufficiently expensive with an impressive reputation for strength to weight ratio so as to make it marketable as exotic.
If you do make Ti alloy knives, look into coatings for the edge. I'd recommend either a PVD coating like TiN or some varient of that type, OR a nitriding process like Nobleizing, which we have done at Flowserve in Tennessee.

Who makes those ? I've seen hammers, but not a crowbar. Could be useful - you don't need much of an edge on it.
Only for saltwater diving, and they're not even very good at that. Titanium knives are, by and large, a bit of a let down.
Depends on the alloy, and it's all going to be pretty low. 6/4 alloy is the hardest you'll get - Google or Machinery's Handbook for the magic numbers.
The one time I've ever heard comment about Ti hardness (and that not positive) is in bike frames. Frames are made of several alloys, cp (pure), 3/2.5 (strongest alloy you can get seamless tubes in) and 6/4 (strongest, but the tubes have to be welded). The 6/4 frames are known for having rear dropouts so stiff and with such surface hardness that you can't get a nut and bolt to grip. Unless you use a fitting done up with a tool, the typical hand-tightened bike wheel locating skewer is prone to slipping out of the dropout if you hit a bump!

Those are only the alloys that are the most common. "3/2.5 (strongest alloy you can get seamless tubes in)" Not true. I use seamless Ti 6-4 in thin wall seamless at 1.5 " OD and 0.032" W.T
"6/4 alloy is the hardest you'll get." Not true. I know of alloys that exceed 200ksi. Higher strength should be possible." I have a piece of Ti 15-3-3-3 seamless tubing 1"od x 0.028 wt that I use for a hiking staff. It has a strength of 186ksi.
"stiff and with such surface hardness..." Not true. The stiffness of Ti is roughly half way between steel and aluminum. You may be confusing stiffness (Young's Modulus, a material property.) with moment of inertia, (a section property.) Hardness is most commonly measured as a resistance to penetration under standardized conditions. That means it varies with strength. The loosening problem you reference can be from a wide variety of issues, not just titanium. Airplanes use millions of titanium fasteners and have for decades. We do not have problems with titanium bolts loosening.

A 200ksi Ti alloy will have reasonably high but inreliable hardness values. Alloy? How about Ti 10-2-3?