My partner and myself will be moving to Arida in March 2017 and need to find an apartment to rent, please can anyone give any advice on how to best achieve this or the names of any rental companies in the city.
Here's some info that might be useful to you, taken from our page on Accommodation in Japan:
It is recommended that expats looking for accommodation in Japan go through a real estate agent as they will understand the local language and be able to provide a list of suitable accommodation to meet an expatriate’s needs. Many landlords are reluctant to rent to foreigners, so it is best to go through an agent, rather than attempting to rent directly from the landlord.Available accommodation is also usually advertised in the local media. If viewing an apartment, it’s a good idea to take a trusted friend or colleague along who is able to speak Japanese, as most landlords are unlikely to speak English.
So you're on the right track in terms of wanting to hire a real estate agent. I don't have any personal recommendations on specific agents, but if you ask around in Facebook groups/pages for expats in Japan, someone might be able to recommend an agent.
Do you have employment and plans for visa applications arranged yet?