We tentatively selected TenCate EX-1543 for use at this sort of temperature. At 400°F (204°C) it's listed as having a shear strength of 1900 psi (13.1 MPa). Its RT shear strength is listed as 28.1 MPa, so it's not the most brilliant performer. However, if your specimens are not unusually thick it should be adequate. We did not get around to actually testing it. As a cyanate ester it's probably quite expensive.
Have you tried the Cotronics products? I've used 4625 with great success. Bear in mind these are mostly epoxies but should work as adhesives for your application.
Graydon Tranquilla P.Eng Electrical
Industrial Oil and Gas Industry,
APEGBC, APEGGA, APEGS, APEGM