Try Insectnet.com as well, it's mostly lepidoptera, but people do list beetles from time to time, I've purchased Dynastes tityus adults, Dynastes granti adults,
and Lucanus elephus grubs, Prices may be less than you might pay at a regular website.
There is a recently imposed one time fee to join, I think it's 10 euro or so, although the site caters to mostly USA trade, it's operators are in the EU.
The fee is designed to discourage scam ads, they used to be a real distraction. Once you're a member, the site is free to use. I've made dozens of contacts
through the site, it's somewhat similar to the Beetle Forum.