Silver solder resists higher temperatures. If you don't need them, just take tin-copper solder used for electronics presently, or the better tin-lead that was used previously (forbidden in Europe now). Their melting point is like +200°C and +180°C. Clean surfaces and good flux are important.
Available from plumbers and their shops.
Other compositions exist(ed) which I haven't used, like cadmium. Must be forbidden in Europe meanwhile.
At maximum +150°C, you can make a mechanical contact, with thermal paste between the parts. Press seriously with screws the precisely matched surfaces.