for your 17' Accord V6, I would use a full synthetic 5W30. I checked the netlube guides for both Castrol & Valvoline & Penrite and they all gave a large selection of their 5W30 oils, of various specifications. Their recommendation needs to be approved by Honda Australia, so you know 5W30 is good to go.
You can go to the thinner end of 5W30 and get something that’s API SN or SP, with ILSAC GF-5 or GF-6 and maybe Dexos1-Gen2. The Euro A5/B5 is also on the thinner side.
Or you can go to the thicker end of 5W30 and get a Euro rated oil with ACEA A3/B4 (full SAPS) or C3 (Mid SAPS)
Some honourable mentions:
Castrol Edge 5W30 that’s A3/B4 and BMW LL-01 and MB 229.5 (high ZDDP anti-wear)
Castrol Magnatec Stop-Start 5W30 that’s API SN and ACEA A3/B4
Castrol Magnatec A5 5W30 that’s API SN, ACEA A5/B5 and Ford 913-D
Castrol Magnatec Stop-Start 5W30 C3, it’s API SN/CF, ACEA C3, MB 229.51, Dexos2
Castrol Magnatec BioSynthetic 5W30, it’s API SN, ILSAC GF-5
Nulon 5W30 Long-Life full synthetic, it’s Dexos1-Gen2
Valvoline SynPower 5W30 DX, it’s API SN-PLUS, ILSAC GF-5, Ford WSS-M2C946-B1, Dexos1-Gen2
Valvoline SynPower 5W30 FE, it’s ACEA A5/B5 and Ford 913-D (thinner than the DX but with more zinc ZDDP anti-wear)
Valvoline SynPower 5W30 MST, it’s API SN/CF, ACEA C3, Dexos2, MB 229.51, BMW LL-04 (thicker again than the other two SynPowers, mid-SAPS)
Shell Helix HX8 5W30 full synthetic, it’s API SN/CF & ACEA A3/B4
Shell Helix Ultra, mid-SAPS ECT 5W30 (ACEA C3, BMW LL-04, MB 229.51)
Penrite Enviro+ GF-S 5W30, API SP and ILSAC GF-6A
Too be honest, I would also be happy with a full synthetic 5W40, like Shell Helix Ultra 5W40 (A3/B4, BMW LL-01, MB 229.5) or Valvoline SynPower MST 5W40 (API SN/CF, ACEA C3, MB 229.51, BMW LL-04, Dexos2, Porsche A40), etc.
You have a lot of good oils to select from in Australia. Like you said, in the USA they probably use 5W20, and you could also use a 5W40, so I would select any good quality full synthetic 5W30 and relax. The difference between the above 5W30 oils, will not matter to you, as your Honda is very robust. I would just buy on price or use what you have.
I try and keep on top of the local sales here, I’ve been a bit slack under COVID though
At Repco in Australia, 14-24 February 2019. Castrol Magnatec 10W40 semi-synthetic, API SN/CF and ACEA A3/B4 is $25 for 5L (save $24) Valvoline XLD Premium 15W40 mineral, API SL/CF is $17 for 5L (save $23)