FIRST, read the reviews of this amplfier in the Review section of eHam.net
SECOND, The Dentron MLA-2500B uses the Eimac 8875 ceramic RF tube. This triode RF tube is not longer manufactured. Here is the EIMAC specification sheet (for your overall education).http://www.g8wrb.org/data/Eimac/8875.pdf
The 8875 uses TRANSVERSE cooling, while its sister tube - the 8874 which Eimac and Svetlana still product today uses AXIAL cooling.
The EIMAC 8874 is readily available and used commercially, BUT they ARE expensive compared to other options.
LASTLY, BAsed on your questions -- I recommend (IMHO)
1, Move on. Tube conversions are possible - BUT this is NOT a begineer project - It requires proficiency and experience in: metal fabrication, High Voltage power supplies and $$$$
2. Your question: "Is there a direct drop in of some other tube that will produce the same wattage or is there a tube conversion easy enough to be done by the owner or is there someone that does tube conversion to amps?"
As I said -- move on.
Tube conversions are fine for builders (and aspect of the amatuer hobby akin to furniture makers in woodworking and Chip Foose in car restoration -- are you a builder?
Lawson, W4EMF and Tony W4ZT are 2 very good ones!http://w4emf.gs35b.com/mla2500-retro-3cx800/index.html
3. IF you want an amplifier (cheap to maintain and support), then look for 4 tubes!
GLASS: 811/572B or the 3-500G
CERAMIC: 3CX800 or 8877