OK, let's define some terms.
You are looking for some way to trigger your Hasselblad and you want to be in the photograph yourself.
You first looked at the pneumatic bulb releases with long tubes, but you are concerned that they will not supply enough force.
Now you are looking at accessory self-timers - mechanical ones that screw into the camera's shutter release.
I think you will find that the compatibility of anything you try will depend on:
1) the shape and size of the unit (if it is too big the lens may interfere);
2) how long the plunger "throw" is; and
3) how much force is exerted by the plunger.
The threads themselves in the camera's shutter release are standardised. The depth of the throw and the force required varies slightly between models of cameras.
Unfortunately, with the exception of the threads, there probably aren't any "standards" out there in respect of the long releases or accessory self-timers. So we would be unlikely to be able to point to one particular model and say "this one will work".
I have a mechanical accessory self timer that is probably at least 40 years old. It is somewhat adjustable, but I find it easy to use with a couple of cameras, and incompatible with others. I don't have a Hasselblad to try it with.
I haven't seen one of these in a store for a long time. If I were to look for one in a store in our area, I would try Leo's Cameras in Vancover.
I wouldn't necessarily give up on the pneumatic bulbs yet - you'll need to find a place though that will yet you try one.
