Jarvis has signed for York while Knill does not expect Howe, last season's top scorer, to sign a new contract after his deal expired.
"We've spoken to quite a few forwards and I have a meeting with one," Knill told BBC South West Sport. "I'm hopeful we'll have more news next week.
"I spoke to Rene last week and I spoke to his agent on Monday, and if I'm honest it doesn't look as though Rene is coming back. We kind of knew at the end of the season that it'd be a position that we'd have to strengthen."