Try equine.com or equinenow.com. It's definitely harder to find a tall WB between those ages under $5K, but it can be done. I've found that sometimes taller horses can intimidate riders and get away with bad behaviour then they are sold as problem horses or mature horses that need to be restarted. There's deals out there right now for a confident, experienced rider willing to put in a little effort.
My sister just bought a 17.2 Imported (from Germany) 9 year old Oldenburg (she copied me, lol) for $4000. He vetted clean but he was for sale because he bucked his rider off and then was left to pasture. He apparently has great movement but was too slow at Spruce Meadows for upper level competition though.
This horse is 9 years old,very very clever, 174cm, jumper,stallion. The horse is with an european and international passpot FEI. If it is interesting for you please contact us. Price is negotiable. More detailes: horses for sale
I have a 9 year old 16.1 TB mare for lease. She's scopey and a great mover just needs schooled as she's been a pleasure horse for about 6-8 months. Has jumped to 3' with a rider, free jumps over 4' without trying. I'm looking to long term lease her (1-2 yrs). If you can't find a horse to buy then maybe you would want to lease until the right one comes along? I can be very flexible with the lease =). Let me know if you're at all interested. If not, good luck with your search!