Tennents is an old lager brewery in Scotland, I used to drink it regularly despite the dodgy tins designs.
Basically it's a typical Pommy 4% lager brewed with UK Lager malt and I'd guess some maize (as used in Stella and Carling) and minimal euro hops.
You could have a fair crack at it using a
Muntons lager kit. They pop up in a lot of LHBSs
I don't think you'd have much luck using a Coopers kit.
Even doing it all grain I'd be shaking in my boots, would look at using 50/50 BB and Weyermann malts, about 20% flaked maize or polenta and Hallertau to around 20 IBU with a lager yeast such as S-189 fermented at 12 degrees and lagered for a couple of weeks. I've read on a few brewery websites that they do a 52 degrees protein rest on the mainstream Pom lagers as well.
As for Fosters, it's made In the UK using all local ingredients but the Fosters B strain yeast, to 4% and it's actually quite a refreshing drop on tap over there, if anything better than the sad Fosters Draught that used to be on tap here till the 1990s. Most Poms still think it's the favourite Aussie beer.
Fosters have rebooted the brand with Fosters Classic, a 4% version and that's crap like you wouldn't believe.