When I needed the same earlier this year I did, via google, find a a Sydney travel agent who said they could. However as they were some distance away and visiting was not easy I ended up using one of the on-line agencies. This worked really well. I used Stan Tours (Central Asia - Visa / LOI
) and they got and delivered by email the required LOI without any hassle. I happily recommend that you consider this option. Note the Russian embassy in Sydney told me an email copy of the LOI was fine for a 3 month double entry but for multi-entry the original is required and Stantours will post this to you if you do need it.
Biggest hassle I had with the LOI is to do with the timings required by the Russians. You can't apply for the LOI until 45 days before the intended start date of the visa and then it takes about 3 weeks to issue. This meant you are nervously waiting just 3 weeks before the start date of your trip to start the visa application - which in turn takes 2 weeks (unless you pay extra for the 2 day turn round). Its a stressful feeling a fortnight out from your big trip not having a critical visa in your hands - but there is nothing you can do about this. having said that staff at the embassy were friendly and helpful and I have not heard of any travellers failing to get their visa's.
Hope this helps - if you need more info about how it worked for me send me a message and we can chat - I'll be back in Australia after Christmas.