Thank you for the replies so far. Waynorth, I will have to try and find some of these more modern examples, hopefully some make their way to this side of the country and into my hands! I guess I should have specified more that I was looking for a wharncliffe master blade too.
Bastid- thank you for the compliment. I find that clip blades with broken tips work well for this modification, and allows me to take a broken $5 knife and turn it into a useful $5 knife. It also has let me work with adding swedges before trying them on my custom knives for others, and I am glad for the learning curve being taken out on these rather than Damascus or other steel!! I can't bring myself to modify an unbroken blade, so keep hoping I can find more broken clip bladed punch knives to get what I want until I try my hands at slipjoints (probably a long time away if my fixed blade endeavours are any indication). I have odd tastes so it is probably up to me to piece together my dream slip joints.