After multiple attempts of trying to secure the parts from Dell AU, or main stream online platforms such as Amazon and eBay, managed to find the parts in the following online stores.
Deal4go (never heard of them) - both heatsinks for cir AUD $60 delivered https://www.deal4go.com/products/large-vr-heatsink-j46j2-0j4…
Unsure why this site can not be access normally, and it is definitely not down https://www.isitdownrightnow.com/deal4go.com.html
Trick to access this site is via VPN (or via Opera VPN) through another country, and click "buy it now" before it times out. They do have an Amazon Store, but only carry the large heatsink there https://www.amazon.com/dp/B09784RS2P.AliExpress, each heatsink is $35, so total of $70 for the set https://www.aliexpress.com/item/1005003091827165.html
As discussed in various ozb R10 forums, these heatsinks are required for those replacing CPU air cooler to Corsair H60 AIO. These OEM parts are extremely difficult to find online. Took about 2 weeks of thorough trawling through online stores, and making enquiry to OEM part sellers via AliExpress
Hope this helps.