Stuck while researching for a core upgrade.

So I was recently hired to a company right at the beginning of their core upgrade project (the guy before me ordered the Cisco hardware then quit) so i have to put the pieces together. I have to get my new switches talking to our old core until I can get the new core in and I have hit a small wall: our old core only goes to 1gig over fiber and I cant figure out what SFPs to use for this.

The old system is a cisco 6509 the new switches are 3850s with C3850-NM-4-10G uplink ports, our fiber in the building is 62.5/125 MultiMode the 3850s are what I need the SFPs for. For now there is no budget to upgrade the fiber so once I get the new cores online the company wants me to try and get 10g off that fiber until I can get it replaced as well. Any advice other than replace the building fiber will be awesome.