You mean those threaded nuts? They are usually sold with the brake line tubing at the store. The tubing is often sold in various lengths. There are a number of different diameter tubes used in braking systems. I'm not sure which size your car needs. Ideally, you should remove the old part first to match up what you need at the store.

Since the tubing stock length at the store may not match exactly what you need, there are tube flaring kits available that allow you to cut the tube to length and flare the new end. Make sure the kit can do double flares.

While we're at it, I should also mention that new tubing should be bent without kinking the tube. It may take some practise until you find a technique that works. Though I've bought a tubing bender, I still sometimes find something round to use as a form for making really tight bends.

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95 E320 Cabriolet, 169K