Bushwalk Australia

Looking to replace the current DIY guy ropes I use as additional attachment points for the tarptent. (sadly the tarptent only comes with two guyropes which is inadequate)

Anyone know any good sources?

I found https://www.snowys.com.au/guy-rope-set-5pcs#details these but they are out of stock until October.

Looking for strong and lightweight with sliders.

I always use guy lines with a dyneema core for zero stretch - lots of os sources. I find a diameter of under 2mm is fine as the Dyneema core is extremely strong. These cords usually have a nylon outer sheath for ease of knotting and often a reflective threads for nighttime visibility. The last lot I purchased was on Amazon - Kelty Triptease Lightline (1.5mm diameter reflective) but have other versions from Zpacks, Extrem Texile etc.

For the cam cleats I have purchased them from https://www.cleats.co.uk/. I find the mini LIne-Loks CL266 work well for thin cords and they also sell some dyneema cord.

We , Tarptent, don't supply extra guyropes or pegs because they would add to the cost to the consumer and many of our customers are very particular about what they like.
The reasoning is like this : why should I pay for those guyropes when I like .... and therefore the ropes that come with are no good to me.
of course there are also those that would prefer just to get something but in situations like this the manufacturer can't always win (if at all...)
BTW, the TT type guylines are the same as the Kelty Triptease

The strength of the guylines isn't the main issue. It's durability that matters more. I use 1.5mm nylon cord when I'm willing to be careful to protect them from abrasion. Otherwise, the thin cord Mark F. posted about is good. Hilleberg provides something similar with their tents (in adequate quantity for the tent, thank you) that also works well. They sell it separately although it isn't the cheapest solution. The type of sliders that Hilleberg uses work nicely with thin cord. They're called micro linelocs or camcleats. They look like this:

I use old kite surfing lines. When I scrap a bar I generally end up with approx 150m worth. Lasts a very long time.