The Contaflexes were made in Europe, where you are, and the Pro Tessars you mention were originally supplied with push on black plastic caps. Why not just source the genuine caps? They won't be expensive and if you contact some of the dealers who actively trade these cameras on eBay it should not be too difficult to procure some. I have the genuine caps with all my Pro Tessars as they came with caps and bubbles. This is generally the easiest way to obtain them, too. Note that the Pro Tessars are also threaded externally for hoods and filters etc. A lot of people do not notice that.
I realise you don't want to pay US postage but lens caps are very compact items. You could also contact Pacific Rim. They have a lot of Contaflex stuff and I'd expect them to stock those items at a reasonable price. Last time I purchased something from them they were happy to arrange a less expensive postage option for me (I'm in Australia, so, from my perspective I suspect you have little to complain about, postage-wise).