Yes, there is a 10BASE-FL module for the 6500 chassis: Cisco part number WS-X6024-10FL-MT (24 ports, each can do 10 half or 10 full duplex, uses MT-RJ connectors, list price US$12,995). As far as I know, there is no dedicated 10FL card for the 4500 series chassis.
The module is rather expensive, for 24 ports of fiber Ethernet. A less expensive and more flexible solution is to use copper ports, and convert media to fiber.
If you have a 48-port 10/100 module in the 6509, you can disable autodetect of speed and duplex on as many ports as you need, and manually set them to 10 half. Then, use a Category 3 or better patch cable to connect to a 10BASE-T to 10BASE-FL media converter.
If you need many 10BASE-FL connections, then instead of a few standalone media converters you should consider a rack-mount solution. There are several manufacturers which make these; Transition Networks is the one I would recommend (http://www.transition.com). They have a rack-mount conversion shelf that hold up to 18 or 19, and the shelves can be daisy-chained for management purposes.
This will be a more cost-effective solution than the module that installs into the 6500 chassis; but the module would be a more elegant solution.
If you don't already have a 48-port 10/100 module in your 6509, you can still buy one and install it. However, if you do have GBIC ports available, it is less expensive to purchase a Catalyst 2950G-24 or -2950G-48 and the GBICs to connect it to your chassis. Then, use the media converter approach outlined above. (Of course, a 10/100 chassis module would be the more elegant solution.)
In general, 10/100 ports are more useful and are a better investment than dedicated 10BASE-FL ports. As long as you need maintain some sort of 10BASE-FL connectivity, they can be configured to serve that purpose now with the media converters. And you can convert just as many as you need. Later, when you don't need them for 10FL, you can reconfigure the ports back to 10/100 auto and use them for something else.
Hope this helps.
