The Enet, USB, FW combo cards were made by SIIG and the part numbers are JU-2Ne012, JU-2NG011 and JU-2NG012. The latter two are gigabit and much harder to find, although there are none of the former on Ebay at the moment. Some Macs do not work properly with PCI-PCI bridges, which is the magic chip which lets a card like this put three PCI devices in one slot, so whether you'll get full functionality from such a card is in question.
For scrolling, a faster CPU or a fast video system are indicated. Depends on which is causing your slow performance. You might try putting in something like a Radeon 7000 or Radeon 9200. G3 ZIFs were made up to 1.1GHz, although those are very hard to find. The 450 MHz is a good compromise between performance and realistic expectations of finding something faster. After that, there are teh somewhat rare 500 MHz cards with copper based G3s with the 10X multiplier, all of which, I think, are IBM manufactured G3 chips. Then there's a big gap before the 800 MHz, 1 GHz and 1.1 GHz G3s, also with chips from IBM, but the actual ZIF is from PowerLogix.
Also, if the hard drive is original, replace it with something, anything, more modern. Even though the ATA interface is only 16 MB/s, Apple's original hard drives in those machines were still much slower than that. Even better is to add a disk interface card such as an Acard AEC-6280M or AEC-6290M (fomer = PATA, latter = SATA) along with a newer drive.