"I'm busy right now." ---> This is 100% correct.
"Get someone else to deal with it." --> This sounds rude, I would not say this unless I was frustrated.
"Find somebody else to deal with it." --> This is 95% correct. I would say "Find SOMEONE else to HANDLE it." Also, a warning, this sentence also sounds slightly rude. If you wanted to be more polite, you could say:
"I would find someone else to handle this."
This sounds more polite and native English speakers won't accidentally mistake your tone as rude. :)
"Deal with it" is usually used on its own as a sentence. Think of this as a fixed phrase, maybe something you would say to stop an argument.
"I don't want to go to school, I'm really tired today."
"Deal with it, you don't have a choice. School is expensive."
Another note - this is also slightly rude/curt. It's best to use this with friends/family who won't mistake your tone.