When it comes to spare parts, the first question is whether that mower is sold under multiple brands, or only by Husqvarna. It pays to check the parts prices from several sources if possible. Then when you know Husqvarna's price, contact the Outdoorking online store and see if they can provide it: their prices are usually better.
The ball joints on the ends of that tie rod are usually called tie rod ends.
It sounds as if one of the things you have to get used to is that some ride-on mowers are intended only to be serviced by experts. Heavy-handed amateurs are likely to use up quite a lot of spare parts while they get the hang of it. Other ride-ons are relatively bullet-proof. I think you've got one of the delicate type, and perhaps your way of handling it has not yet been altered to suit that machine.
