Hi
Helen,
I have had a quick scan of the net to try and find a suitable supplier of Microlaena seed but have not seen one.  I know of one operator who is attempting to develop their own sources of seeds for species like this but it is still in early stages. 

Indigenous Nurseries will also tend to have a very strong position on provenance and will be reluctant to see stock go to areas outside of a limited range.  Unlike some other grasses, Microlaena exhibits marked variation in different parts of its range so stock from a commercial supplier from NSW would be unsuitable for supplying in Melbourne.  Greening Australia (Victoria) may have information on suitable local seed suppliers. 

I have a few suggestions.  Apologies if none of these fit your schedule or scale of your project. 

1. Order a few trays of the Microlaena Envirocells/speedlings- these are small plants about half the price of tubestock and available from VINC and other nurseries, especially if you give notice.  Plant these in a favourable position this autumn and collect the seed in the following season (December-January) yourself.  The plants tend to grow and seed vigorously in their first year if planted in a moist site. They are very easy to collect from, the seed tends to be tinged purple when ripe and detaches easily when the stems.  I collect from plants in my own backyard and manage to collect several thousand seeds (about a litre) over a 6 week period, collecting once a week.  (before you ask, I am afraid I have already passed on this years supply!) . 
2. A variation on this is to do very good weed control across your whole site and plant the cells thinly- perhaps at 4 per metre square.- they are prolific self seeders and if you can keep the weeds down then they will thicken up in a couple of years.  Austrodanthonia racemosa is another excellent lawn grass that will cover ground rapidly in this way and if combined with Microlaena will extend the environmental conditions the lawn will withstand. 
3. Most stands of this grass will have already finished seed production but sometimes there is a smaller flush of seeding following autumn rains.  Stands beside a river may persist in seeding thorughout even dry periods.  A local Friends group may know of a stand that you might gain permission to collect from- it notice it persisting in many peoples lawns when they forget to mow.

Good luck, it would make a useful article to provide an update on where the supply of native seed is at. I will try to do some more in depth research on this to add to an Indigenotes, please be in touch if you find out any information that you can share. 

Regards,
Brian Bainbridge
President, IFFA