Welcome to THR, Pelleman and congratulations on an extraordinary (at least by US price standards) bargain on the Dan Wesson.
IMO, the idea of using a "liquid metal" product to cast a temporary substitute barrel wrench is one that will likely disappoint you in practice. I very much doubt that one would be able to withstand the torque loads generated in use without breaking. While those loads aren't of a large numerical value, relatively speaking, they are concentrated on two points with very small surface areas. I do not think that any such non-homogeneous composite product would be up to the task.
If you can't get a wrench from CZ for some reason at this time, you might want to try The Gun Parts Corp. (
www.gunpartscorp.com) here in the USA.
While they do not always have them in-stock in sufficient numbers for inclusion in their catalog, they often have a few on-hand. They will ship internationally, subject to conditions which should be listed on their website.
Another option would be through one of the dedicated Dan Wesson websites. You may be able to purchase one from a private party that way. There are also auction/sales websites here such as Gun Broker.com where one might be found. Worth a look, anyway.
The barrel/cylinder gap can be set properly with a simple "feeler" gauge of 0.005-0.006" thickness. You can work out the metric equivalent at your convenience.
FWIW, you can almost certainly find a selection of aftermarket grips for your DW at one of the above mentioned sites, too. While I'm not familiar with Swedish/EU laws regarding importation of firearms parts or accessories, I'm sure that you should be able to find some way to get such relatively innocuous items as a wrench or grip without too much trouble or expense.