Geeeezus, i’ve never considered that pairing, to be honest, I can SLIGHTLY understand the attraction there since im an avid Snape/Hermione fan (older guy/younger girl thing, hehehe) but i dont know how much luck you’ll have – my fave fanfics site would be: http://www.fanfiction.net/book/Harry_Potter/
If you didn’t already know, you can choose which characters you want to find fics on, so you could TRY Arthur/Hermione, im just not sure how you’ll go with ur search, good luck! 
Geeeezus, i’ve never considered that pairing, to be honest, I can SLIGHTLY understand the attraction there since im an avid Snape/Hermione fan (older guy/younger girl thing, hehehe) but i dont know how much luck you’ll have – my fave fanfics site would be: http://www.fanfiction.net/book/Harry_Potter/
If you didn’t already know, you can choose which characters you want to find fics on, so you could TRY Arthur/Hermione, im just not sure how you’ll go with ur search, good luck!
References :
my own personal experience in reading a gazillion HP fanfics! lol
p.s For the ‘fiction rating’ choose ‘M’, you’ll be more likely to find something.