You didn't look hard enough in the DIPTRACE libraries. If you search for 74123, you'll find the part. The SN74123N is the one to pick. The HC parts are a just high speed CMOS, but they have the same pinouts as the TTL parts.
Part of the magic of parts is knowing that the different technologies are all the same pinouts as a rule. When you're looking for something like the 74XXnnn part, for instance, search on the 74nnn part instead and you're more likely to find it. Sometimes, especially for surface mount, the proper footprint isn't available. Then you can simply find a part with the proper footprint and graft the two together to create the necessary part. I don't usually have to create a footprint, but for certain parts I have had to do that. Once you do a few, it gets pretty easy.
