Where can I get a good set of jump boots?

Im not Airborne, but I have plenty of experience with foot issues. Never ever buy used footwear. The previous owner of that footwear will more than likely have a completely different foot impression and if your foot is nowhere near that same impression, then all you will end up doing is causing more foot problems down the road.

You can buy decent used ones at Yadkin boots. You'll wear them once a month, do it would take years to break in a new pair, plus a used pair just shines up better. Yadkin boots will also shine them up for you with that high luster base coat that's easy to maintain.
I recommend you take your field boots there and get the SOPC special for about $80. They'll cut out the toe and heel cup and replace the sole with a softer midsole material. Not great for traction, but amazing for ruck marches and day to day wear.

I would NEVER buy a pair of used Jump Boots. Think about it this way - Would you buy someone's used Low Quarters?

Next, I would purchase Corcoran brand boots. From my understanding they are now priced at about $120 at one of the previously mentioned locations, which is less expensive than they were when I retired in 1996. To put this into perspective, I bought only 2 pairs of Corcoran Jump Boots, the second pair I bought in 1982 in the PX there at Ft Bragg, they cost me $125. I know that you could purchase them today in a civilian store for about $170.

Those boots if taken care of will last a lifetime. The pair that I bought in 1982 are in excellent condition, kept polished and are worn on occasion, much less than 20 years ago.