Daylight-loading tanks are no longer manufactured. The only sources are auction sites (particularly eBay), photographic collecting fairs and the like.
Before buying you will need to check that all the parts are included. The seller is often unaware of what should be present. Study the manuals (download from the MANUALS page above) which show photographs of the parts and if full photographs are not shown by the seller, then ask if all parts are present. The item most likely to be absent is the film guide, but damaged belts, clips and the absence of the metal tongue in the lid of the Rondinax 60 are also seen.
The older bakelite tanks are sometimes broken. If edges are missing around the light seals, that part is useless. Sometimes parts have been broken and glued back together. Such tanks are usable but hot water is best avoided!
Advice on the sealing washers that prevent leakage is shown on the Blog Page (28 October 2013).
In general, tanks for 120 film (Rondinax 60, Kent 20) fetch higher prices than those for 35 mm film (Rondinax 35, Essex 35). The Rondix is rarely seen offered for sale.
THERE IS LOTS OF ADVICE FOR BEGINNERS ON THE BLOG PAGE