John,
Amongst my collection of loads I have an air-cooled Vectron DL-650M, which will take 1.5 kW for 10 s, 500 W for 40 s and about 200 W indefinitely according to the de-rating curve on the side. It's quite good to UHF in its frequency characteristics but one weakness is that the slotted box is relatively leaky from the RF viewpoint. However, that's sometimes a plus in putting together an effective monitor arrangement.
You might also be able to pickup a used better quality unit such as Bird 500-WA or WT series air-cooled attenuator or dummy load ("coaxial termination"). One of my more useful bits of test gear is a Bird 300-WA 40 dB power attenuator which is effectively a dummy load and which, when teamed with a small external supplementary attenuator (10 dB) makes for a nice accurate spectrum analyser interface (e.g. 100 W in giving 1 mW out).
73, Peter.