A few weeks ago I emailed Jerry, W5JH, who makes the Baby Black Widow paddle kits for the Elecraft KX1 and QRP Kits PFR3 to ask whether he had considered making one for the very similar HB-1A. He asked for some measurements which I duly sent and he produced a prototype which attaches to the steel case of the radio using magnets.
The cost will be $42.50 plus shipping. However, Jerry needs at least 10 HB-1A owners to commit to purchase. He posted some information about the key in the HB-1A users Yahoo group but there is no evidence so far of any interest from members (though it's possible some emailed him directly.)
I think that a paddle that attaches to the HB-1A would be a great accessory for use in the field and it would be a shame for this product idea to be stillborn for lack of interest.