1 where or how do i get 1???
If it is a straight roadworthy certificate you will only need to find a workshop licenced to work on LPG systems. Phone book? It will cost a bit more than a standard certificate but not much.
#2 Does running ur v6 on gas do damage to engine
Potentially, running on LPG can be hard on valves both the seats and the guides. It's a temperature issue so worst at sustained high speed and load. Using a memcal (and wiring it in to the fuel changeover switch) from the factory approved system will add some petrol while running on LPG at high loads for cooling. There is no need to be concerned if you don't have it with a car of the age of a VS - it takes a lot of km's for any damage to occur, especially if you're not planning any high speed runs through NT - the rest of the car will probably fall apart first.
The LPG memcal also has a seperate ignition map for when running on LPG. This also minimises the valve wear (retarded ignition timing causes hotter exhaust valves).
It helps to run on petrol occasionally; something like half a tank a month. That also avoids any problem with petrol deteriorating from being left in the tank for an extended period of time.
An engine on any fuel running at less than optimum tune will wear faster. Given the nature of LPG fuel systems it is more likely that they will be running at less than optimum tune but there isn't anything inherent with LPG that means it
has to be less than optimum.
There can be a greater tendency for acid build up in the oil - also a temperature issue - and higher running temperatures tend to lower oil viscosity under the conditions which the engine is actually running. There are oils specifically designed to cope with those issues but using an oil with a viscosity range on the higher end of those recommended and changing it at shorter intervals is an alternative.
The spark plugs should be changed and the leads checked every 20K km - LPG is more sensitive to ignition problems.
It helps to have a cooling system that is in good condition.
If the engine does die, replacements aren't hard to find and should be under $1K fitted.
#3 or should i just pull gas out??? Dnt know wot 2do neva had a car on gaz b4
Nope. That will cost you money (or at least time) to do and your fuel bills will double. A typical Commodore might use ~$2400 per year of petrol - 20K km, 10l/100km, $1.20/l (you can do your own maths for your car and its use - factor in +30% consumption on LPG). Including the cost of using a small amount of petrol, $1200 buys a lot of repairs on LPG even if they were to be needed.