I would say that when a company issues a bond, it will do so using a broker and not sell directly to the public. If you have an account with a broker you may be able to get included amongst the buyers but you would need to be investing a hefty sum as they are not really aimed at the general public.
If the bonds are listed on the Stock Exchange, you could buy them there but again the minimum deal may be set quite high
There are a number of EFT in corporate bonds, for example iShares IE00B6X2VY59 but they all come with a word of warning to Irish resident investors because of the Exit tax regime