Lovely bike! Because this model Triumph was built in such large numbers, you should have no problem with the missing parts.
"I want to keep it in this state." Excellent idea; it looks great like it is.
"The painting of the tank is it original?" No, but it looks great like it is! The TRIUMPH logo is from a later model bike.
"I am looking for some missing parts:
The black part of end of the advance ignition handle (see foto)" You might have to make one, or have one made. Some of the modern plastics look very similar to the ebonite end. Keep an eye on ebay for a lever with an original end.
"Tire size" 26 x 2 1/2" beaded edge. The Ensign tyre is a popular one at the moment.
"The size of a ball bearing wheels" All the balls are loose in the cycle parts: wheel bearings, steering head bearings, lower fork bearings (where the fork rocks back and forward). Measure up a sample - you can buy good quality steel balls on ebay.
"A front rim" Vintage rims in New Zealand do a nice beaded edge rim, and can drill to match your original, or try
http://www.veterantriumph.co.uk/ "The wheel nuts front (or dimensions)" Be careful here. I think the threads are 20 tpi, but they are a cycle thread form, and NOT UNC. Ordinary nuts of this form are on ebay, or try
http://www.veterantriumph.co.uk/"Nut rear wheel (or dimensions)" See above
"What oil to use?" I use a simple 50-weight oil in my early bikes - not too many additives.
"Is that there are professional reproducing parts?"
http://www.veterantriumph.co.uk/Good luck! Make sure you clean out the motor quite thoroughly before you try to start it.
Leon