Is there a redstone device that can gather lava buckets hands off?

If you are getting buckets spat into the lava pool, it is either because you are dispensing buckets using a dropper or because you are dispensing them into flowing lava instead of source blocks.

Unlike water, lava doesn't create source blocks. This means you can't create infinite lava sources like you can with water, and unfortunately you cannot automate the full process.

You can, however, semi-automate this process by creating a system where you use one bucket to transport the lava between the lava lake and the machine, and the machine will fill each bucket from an input hopper. You can check out many tutorials online to help you with this, or see if you can find a bug online that can help you create an infinite lava source.

The only option to automatically fill a bucket with lava is using a dispenser, from lava source right in front of it. The dispenser can't be moved (in front of next lava source) in vanilla Java Edition, and the lava source can only be moved using buckets (potentially with (immovable) dispensers). So, in short, "no". You can't truly automate the process of gathering lava.

What you can do though is to automate transport. A minecart line, automatic loaders/unloaders, sending empty buckets back, even means of sending the carts through a portal to the overworld and keep the overworld part loaded. You'd only need to fill the buckets and put them in a chest of the loading station right next to the lava lake.

On the other hand, the Carpet Mod provides movable tile entities. That means you could build a flying machine that harvests a lake of lava through use of a moving dispenser.

I know that this isn´t a direct answer to your question, but it can solve your fuel run problem. You can make a simple automatic observer piston farm with sugarcane or kelp (Because they grow fast) and let a water stream feed your plant material into hoppers into your furnaces or whatever you want. The only problem is that it has to be big enough and can be an eye sore.