Muntons make a bock kit but it's super hard to get, even from HBS, may have to get it specially ordered in for you
and promise to take minimum qty which is usually 3 cans, or pay the freight and get it mail-ordered from one of the site sponsors.
At OG of 1042 it's 'bock style beer', not true Bock, so a 2 can with a can of liquid malt might go close
to the 7% target of a true Bock.
I made this a few years back and it turned out quite good:
1 can Coopers Bavarian lager ( or substitute European lager now )
1 can Light Liquid malt ( 1.5 kg )
0.5 kg Light Dry Malt
Mini-mash of:
0.5kg Vienna
0.5 Crystal malt
30g Halletau hops boiled 20g @ 40 min, 10g @ 20 min.
I was slack and used 2 sachets of Coopers kit yeast
Fermented at 15 deg for 3 weeks.
The purists will say not to put crystal into bock and they are right, but for an inexperienced masher it's an easy way to get some good colour and caramel from grain. It made very nice beer.
My next effort was a two can of bavarian lager with extra hops and liquid malt and it was a flavour disaster
that may have been caused by oxidation.
I don't feel you can get even half decent bock from a straight kit and kilo, but then I've never been able to get hold of the Muntons bock kits. These will be expensive, but good bock is worth every dollar.
I'd make a single can kit and kilo first at about 5% abv to get the hang of it,
then up the fermentables and go for the 7% and true to style. If the OG isn't 1065
then it won't be in the style.
You may have just started my next quest - to make a good proper Bock.