As far as I know, you can get nearly any aftermarket alarm to work with smartlock. Its not the brand of alarm, but rather the person that is doing the installation that matters more.
(I.E. to intergrate with smartlock, the installer needs to have some knowledge on how the smartlock system works).
Also many of the cheap alarms fail because of poor installation, (IE one of the easiest places for an alarm to be installed is near the steering column, due to the close proximity of Ignition and power lines. - Not very good, as the first place a theif looks to try and hotwire a car is there !!!)
Sometimes alarms have very poor short circuit protection, (I.E. one very common brand a number of years ago, could be disabled completely by shorting one of the blinker/hazard bulbs on the outside of the car)
Anyway, back on to the smartlock system.
If you think of the Smartlock system as having 2 distinct and seperate parts, then you get a better idea of what I am talking about. One part is the remote keypad, with lock/unlocking and boot release, and the second part to the system is the engine immobilisation. Both are completely independant of each other.
As for the single keypad thing, you can program smartlock to ignore the original Ford keypads, and then wire any alarm up to the central locking, so as you still have smartlock doing the ECU cutout with the ignition switch, and have the aftermarket alarm doing the remote door locking and unlocking, alarm, and simple ignition cutout duties.
The only real (Cosmetic) issues with adding an aftermarket alarm is getting the interior light to switch on when disarmed, and off when it is armed. (Instead of just waiting for the lamp to come on after the door is opened, and waiting for the lamp to switch off after the light delay has finished.) Many installers would either not know how to do this, or simply could not be bothered, due to the time required.
I got the Jaycar LA-260 ($199 from Jaycar) to work perfectly with mine (EF-Including Interior light delay, anti hijacking, boot release, etc, etc), and also added further modules to allow the windows to automatically wind up when the alarm is armed. (I also did a lot of other work with the smartlock, and the alarm to get a number of other things working and make the system more secure, but I dont really want to discuss that on the web.)
There are 2 places in Sydney that I would recommend, both know their products inside out.
AutoMicro in Kograh. (Based on Princess highway, just up from Uncle sams service station).
H & H Security. (based in Clovelly - though I am not sure if they are currently installing car alarms ???).
Both have a number of models available, (from cheapo immobolisers to pagers and quicktrack style alarms).
As for places in Melbourne, I can't say that I know of any, but I am very sure that there are some very good places there as well.
Hope this helps