I think your best bet is to try and excavate the stop c*ck in your front garden.
If the brick lined shaft is less than an arms length then hopefully you can get your arm down ( but you may find yourself excavating with a teaspoon).
If the shaft is too deep, then bite the bullet and dig around it - you need to be able to turn the water off in an emergency so this does need fixing. If it is the water board's stopcock then presumably they should fix it. If it is yours then the water board need to turn the water off for you whilst you replace or fix it.
There may be a stopcock under the pavement (if tarmac, then it could be buried). Metal detector could be the only way to find this. I presume the water board would know, and if the stop c*ck is buried then it is probably their responsibility to unearth it.
For the inside tap, you are snookered unless you can disable the mains. The only way that occurs at the moment is to use a freezing kit on the mains input prior to the stop c*ck, cut out a length of pipe and fit a new stopcock. Then remove the old one and redo your pipes. However this is well dodgy as if you get it wrong you have a gusher and no way to stop it.
HTH Dave R