You would be lucky to find one. Most trailer buying cycles are 10 years so none of the big boys will have them for sale at the moment. Plus, most LSTs were either curtains, deckers or boxes. Throw in the fact that most flatbed work tends to include a lot of weight and there was and will still be little demand for them.
In fact the only ones I’ve seen on the road were step frames with the pallet boys or hay guys. Most hay guys use wagon and drag though and run the kit until the wheels fall off.
This might be one you will need to get built specifically for your requirements.