Where can I get a Type T 6.3 AH 250V fuse for a K3000FX 300Watt Keyboard Amp?

SOURCE: blown fuse and replaced it and burned the amp

BIG problem! You should NOT have replaced the fuse as additional damage has been done. I repaired a PMP5000 and I can tell you likely what you will find: The smoke and smell came from two power resistors that are part of the soft start circuit that now are toast. You will likely find several components in the main portion of the power supply that are toast. These will include transistors, resistors, diodes, and probably the small 8 pin switching regulator chip. There is a small power supply that comes on first which enables a relay that shorts out those soft start resistors AFTER the power amplifier BALANCES and normalizes.
The unit I repaired had severe damage due to arc-over at one power amp section. Three power transistors were destroyed there and board traces and charring had to be handled in that section.
The repaired unit had to be brought up with a light bulb in series with the line power cord to prevent further damage until all bad parts were discovered and repaired. You will need to take the unit to a shop that is expperienced with the product. The repair cost MAY be pretty high.

SOURCE: I own a Behringer Ultratone

This is most LIKELY an electronic problem... possibly in the final power amp. Repair may be a simple failed component or a mass number that fail like a stack of dominos. Take it to a shop for repair.

SOURCE: Fuse blown on Europower PMP

You don't need to use a ceramic fuse if one's not available. You can also use a glass cartridge fuse as well. Just be sure the rating is the same. Be aware, though, that fuses seldom blow on their own. Usually it's because something else has shorted. So don't be surprised if replacing the fuse only results in another blown fuse. Behringer stuff is notoriously cheap and under-protected, so by the time the fuse blows it's usually more trouble than it's worth trying to fix. But maybe you'll be lucky and it will be something simple. Good luck, and thanks for using Fixya!