For tourist visa
the easiest way is to have a fully organised trip booked. Never mind, you will not be bothered by it, you just need to include the voucher with the visa application, to show that you are fully cared for during your stay in Russia. Once inside, nobody bothers with it. If you have the visa, nobody cares about the paperwork that precedes it.
So, find an agency that can provide the full service of obtaining the voucher and arranging the visa application. Of course this costs some money, but saves a lot of hassle.