You may go to a different parish for any reason you like. It’s OK.
You might talk to this priest, first, though. This may be a temporary measure meant to keep from spreading some local epidemic or pandemic. In that case, you may be willing to re-think how important it is to you to exercise your right to receive on the tongue. Having said that, you may also remind your pastor–all due respect being assumed–that reception on the tongue is your right, as per the Instruction Redemptionis Sacramentum. He has no authority to deny you that right, nor to even imply that he has that authority, but may only ask you and others under his care to voluntarily receive in the hand because you discern his reasons to be compelling.
In any event, charity may compel you to agree to his request (or it may not, I’m not arguing that point, because I don’t know the gravity of his reasoning), but canon law will not. The law is on your side:
[92.] Although each of the faithful always has the right to receive Holy Communion on the tongue, at his choice, if any communicant should wish to receive the Sacrament in the hand, in areas where the Bishops’ Conference with the recognitio of the Apostolic See has given permission, the sacred host is to be administered to him or her. However, special care should be taken to ensure that the host is consumed by the communicant in the presence of the minister, so that no one goes away carrying the Eucharistic species in his hand. If there is a risk of profanation, then Holy Communion should not be given in the hand to the faithful.
In our parish, it is being asked that we receive Holy Communion in the hand, because we have already had one funeral for a relatively young person who died of H1N1, and because the pastor learned that people can be contagious for a day or more before symptoms make them aware that they are a danger to anyone else. (Holy Communion under the species of wine is also not being generally offered to the faithful.) The request, however, is very clearly worded that way: the faithful are being asked, not told. No one has said that communicants will be refused to exercise their right to receive Holy Communion on the tongue. Because of the particular gravity of the reason behind the request, the pastoral decision to discourage Holy Communion in the hand for a limited time is permissible…or at least, this is what I understand our archbishop to have decided for our diocese at present. IMHO, asking the faithful to forgo something that is a right is a matter with enough gravity that a priest who has the ability to be in contact with his bishop about his particular situation would be well-advised to do so.