I am after some advice, please be gentle with me

We bought our bongo - Bertie, last summer, his has a set of 17" aftermarket alloys on him at the mo, much as these look pretty sweet, i'm driving around with no spare, a slow puncture and tyres that are pretty much on the verge of need replacing!
the speedo is a fair way out which goes without saying, and i'm struggling to find out where i could get a spare 17" for the Bongo from!
Having looked at the price of tyres to replace the ones i have, its not far off the price of a deal with a new set of 15" rims and tyres as a package. I'm thinking not only will this sort the speedo and milage out but handle better also.
I am on the understanding there are 2 variations of wheels? which would i be looking for and how do i find out? Also any recommendations for places / sites that sell new rims for Bongos? Tbh i'd rather have something aftermarket that look real nice than standard Mazda alloys. Bertie is a '95 model
Thanks in advance for any help and advice guys and girls
