Sometimes "sourcing an item elsewhere" is not an option. There was a time when eBay was about rare collectibles rather than Chinese disposables.

OP, is the seller in Australia, or do they definitely ship to Australia?

What is the item? Not that we can change anything, but we might be able to speculate on the reason.

There's an extremely high probability that as well as being blocked, the seller is not receiving any messages from you. If this is the case (and I strongly suspect it is) they would have no idea that you're messaging. Instead of receiving "many messages"  as you imply, they would have actually received "many nothings" from you.

Since eBay sellers don't try to contact other members randomly without reason, I don't know why you'd expect them to try to contact you. Such expectation is rather bizarre.

You ask for advice... don't get your knickers in a twist over something which is out of your control, scroll on by and source your item elsewhere.

"Dear Community can anyone give some advice please"

Why on earth would you want to purchase from a seller  who won't repond to your messages ?

IF by any chance you're on the seller's blocked buyer list, there's an option "Don't allow blocked buyers to contact me"

Is your message actually being sent ?

If that's not the case and it's a buyer requirement  / settings block,  what message are you receiving when you try to place a bid?

@parrahun

Unfortunately there truly isn’t anything we can do; neither can eBay.

Nothing about your feedback (both given and received) raises alarms to me.

But getting straight to the issue of not being able to bid or buy from the seller… If a seller has blocked you, it might be a general block (seller won’t send to or communicate with buyers based on buyer geolocation, or based on NPB strikes), or a specific block (seller has either had an interaction with you previously and added you to their list of blocked buyers, or has added you as a result of indirect information). 

So… is it possible that any of these apply? If you haven’t paid for two items over the last six months, you could be blocked from purchasing from any seller with the relevant buyer requirements set up. Or… If you’ve previously interacted with the seller from whom you’re trying to buy now, that seller may (for whatever reason) have decided to block you and disable contact. Or… the seller doesn’t sell to buyers in certain countries or states. (Blocked contact may still apply.)

Buyers can only ever have 100% feedback, so that is moot

IF the seller has you blocked from bidding, eBay is not going to make them sell to you, so pointless to contact them

And if you have tried ‘many times’ (ie spamming them) that is also unlikely to help

Sellers have no obligation to respond to potential buyers' requests.

I would usually respond unless it was a lowball offer or set off other red flags, in which case I would apply the 80/20 rule.