I don’t know of a supply house that sells those parts.
Not using the electric water heater for 1 month should yield $20-$25 in savings on electric bill. Use a pot heater or immersion heater to make hot water in mean time.
Eventually the savings will yield enough for new water heater.
Check local box store for 120Volt 20 gallon electric water heater.
My local Lowes store sells new 240Volt electric water heater for $200+ > but I suggest getting 10% off coupon and then negotiating best price. Call around for competitive pricing.
Ask for scratch-n-dent models.
Call local plumbing supply.
Call the mobile home suppliers > they might have cheap 120Volt water heater.
I keep saying 120Volt heater because they are smaller and cheaper.
Most box stores install electric water heater + additional parts.
The water connections will probably need to be replaced. That figures another $35 in parts. Plus a bit more on installation. Plus more if the old pipes are rusted out or filled with sediment.
The wiring will still be good as long as house is up to code.
For example if parents house has knob-n-tube wiring and 60 amp service panel, the local code may require upgrade of service. Which is good argument for installing the water heater yourself.
If wiring is not up to code, then water heater can be connected to 120Volt circuit (instead of 240V) and heater will heat water more slowly, but service panel will not get over-amped.
SO if you decide to take weekend and install the water heater yourself, then be sure to take camera with you.
Then post questions and photos on this forum. Once plumbers can see specifics, they can give clear instructions how to proceed.